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 $47.98   12.723%   $54.0845   $54.08   $54.10   $54.10  
  Purchase #2 $95.83   9.565%   $104.9961   $105.00   $105.00   $105.00  
  Purchase #3 $69.90   8.145%   $75.5934   $75.59   $75.60   $75.60  
  Purchase #4 $229.62   4.311%   $239.5189   $239.52   $239.50   $239.50  
  Purchase #5 $66.66   11.620%   $74.4059   $74.41   $74.40   $74.40  
  Purchase #6 $223.81   3.243%   $231.0682   $231.07   $231.05   $231.10  
  Purchase #7 $94.65   10.846%   $104.9157   $104.92   $104.90   $104.90  
  7 purchase totals = $828.45       $884.5827   $884.59   $884.55   $884.60