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 $238.59   11.180%   $265.2644   $265.26   $265.25   $265.30  
  Purchase #2 $91.98   10.344%   $101.4944   $101.49   $101.50   $101.50  
  Purchase #3 $102.88   6.535%   $109.6032   $109.60   $109.60   $109.60  
  Purchase #4 $199.50   5.748%   $210.9673   $210.97   $210.95   $211.00  
  Purchase #5 $231.47   5.769%   $244.8235   $244.82   $244.80   $244.80  
  Purchase #6 $66.33   6.635%   $70.731   $70.73   $70.75   $70.70  
  Purchase #7 $32.98   5.470%   $34.784   $34.78   $34.80   $34.80  
  7 purchase totals = $963.73       $1,037.6678   $1,037.65   $1,037.65   $1,037.70