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 $58.40   4.678%   $61.132   $61.13   $61.15   $61.10  
  Purchase #2 $9.36   11.830%   $10.4673   $10.47   $10.45   $10.50  
  Purchase #3 $227.46   13.230%   $257.553   $257.55   $257.55   $257.60  
  Purchase #4 $6.96   10.181%   $7.6686   $7.67   $7.65   $7.70  
  Purchase #5 $225.33   4.342%   $235.1138   $235.11   $235.10   $235.10  
  Purchase #6 $101.67   3.623%   $105.3535   $105.35   $105.35   $105.40  
  Purchase #7 $169.64   4.464%   $177.2127   $177.21   $177.20   $177.20  
  7 purchase totals = $798.82       $854.5009   $854.49   $854.45   $854.60