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 $218.71   10.544%   $241.7708   $241.77   $241.75   $241.80  
  Purchase #2 $97.41   8.797%   $105.9792   $105.98   $106.00   $106.00  
  Purchase #3 $113.36   3.485%   $117.3106   $117.31   $117.30   $117.30  
  Purchase #4 $36.28   8.605%   $39.4019   $39.40   $39.40   $39.40  
  Purchase #5 $93.55   13.767%   $106.429   $106.43   $106.45   $106.40  
  Purchase #6 $201.88   7.283%   $216.5829   $216.58   $216.60   $216.60  
  Purchase #7 $76.85   9.470%   $84.1277   $84.13   $84.15   $84.10  
  7 purchase totals = $838.04       $911.6021   $911.60   $911.65   $911.60