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 $85.79   7.741%   $92.431   $92.43   $92.45   $92.40  
  Purchase #2 $202.69   12.317%   $227.6553   $227.66   $227.65   $227.70  
  Purchase #3 $210.41   11.349%   $234.2894   $234.29   $234.30   $234.30  
  Purchase #4 $108.78   11.496%   $121.2853   $121.29   $121.30   $121.30  
  Purchase #5 $101.97   9.355%   $111.5093   $111.51   $111.50   $111.50  
  Purchase #6 $28.60   9.417%   $31.2933   $31.29   $31.30   $31.30  
  Purchase #7 $236.94   3.121%   $244.3349   $244.33   $244.35   $244.30  
  7 purchase totals = $975.18       $1,062.7985   $1,062.80   $1,062.85   $1,062.80