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 $91.79   3.179%   $94.708   $94.71   $94.70   $94.70  
  Purchase #2 $123.40   8.455%   $133.8335   $133.83   $133.85   $133.80  
  Purchase #3 $135.88   9.871%   $149.2927   $149.29   $149.30   $149.30  
  Purchase #4 $226.57   4.609%   $237.0126   $237.01   $237.00   $237.00  
  Purchase #5 $151.74   11.348%   $168.9595   $168.96   $168.95   $169.00  
  Purchase #6 $119.72   6.438%   $127.4276   $127.43   $127.45   $127.40  
  Purchase #7 $32.72   8.648%   $35.5496   $35.55   $35.55   $35.50  
  7 purchase totals = $881.82       $946.7835   $946.78   $946.80   $946.70