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 $139.68   6.108%   $148.2117   $148.21   $148.20   $148.20  
  Purchase #2 $230.41   8.694%   $250.4418   $250.44   $250.45   $250.40  
  Purchase #3 $209.57   5.862%   $221.855   $221.86   $221.85   $221.90  
  Purchase #4 $126.29   5.565%   $133.318   $133.32   $133.30   $133.30  
  Purchase #5 $59.94   7.656%   $64.529   $64.53   $64.55   $64.50  
  Purchase #6 $83.65   3.428%   $86.5175   $86.52   $86.50   $86.50  
  Purchase #7 $187.55   13.152%   $212.2166   $212.22   $212.20   $212.20  
  7 purchase totals = $1,037.09       $1,117.0896   $1,117.10   $1,117.05   $1,117.00