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 $163.53   12.322%   $183.6802   $183.68   $183.70   $183.70  
  Purchase #2 $70.69   13.649%   $80.3385   $80.34   $80.35   $80.30  
  Purchase #3 $61.90   11.500%   $69.0185   $69.02   $69.00   $69.00  
  Purchase #4 $230.59   11.700%   $257.569   $257.57   $257.55   $257.60  
  Purchase #5 $179.63   12.148%   $201.4515   $201.45   $201.45   $201.50  
  Purchase #6 $193.80   10.759%   $214.6509   $214.65   $214.65   $214.70  
  Purchase #7 $91.80   8.616%   $99.7095   $99.71   $99.70   $99.70  
  7 purchase totals = $991.94       $1,106.4181   $1,106.42   $1,106.40   $1,106.50