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 $84.56   5.185%   $88.9444   $88.94   $88.95   $88.90  
  Purchase #2 $244.79   7.791%   $263.8616   $263.86   $263.85   $263.90  
  Purchase #3 $20.95   7.651%   $22.5529   $22.55   $22.55   $22.60  
  Purchase #4 $201.71   4.774%   $211.3396   $211.34   $211.35   $211.30  
  Purchase #5 $92.33   11.315%   $102.7771   $102.78   $102.80   $102.80  
  Purchase #6 $9.67   3.247%   $9.984   $9.98   $10.00   $10.00  
  Purchase #7 $59.83   4.870%   $62.7437   $62.74   $62.75   $62.70  
  7 purchase totals = $713.84       $762.2033   $762.19   $762.25   $762.20