Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.86   13.348%   $184.5986   $184.60   $184.60   $184.60  
  Purchase #2 $214.73   6.859%   $229.4583   $229.46   $229.45   $229.50  
  Purchase #3 $134.40   12.120%   $150.6893   $150.69   $150.70   $150.70  
  Purchase #4 $212.58   12.759%   $239.7031   $239.70   $239.70   $239.70  
  Purchase #5 $105.87   10.364%   $116.8424   $116.84   $116.85   $116.80  
  Purchase #6 $184.74   12.730%   $208.2574   $208.26   $208.25   $208.30  
  Purchase #7 $95.60   9.584%   $104.7623   $104.76   $104.75   $104.80  
  7 purchase totals = $1,110.78       $1,234.3114   $1,234.31   $1,234.30   $1,234.40