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 $24.65   3.556%   $25.5266   $25.53   $25.55   $25.50  
  Purchase #2 $122.46   5.628%   $129.352   $129.35   $129.35   $129.40  
  Purchase #3 $247.66   11.130%   $275.2246   $275.22   $275.20   $275.20  
  Purchase #4 $20.33   6.179%   $21.5862   $21.59   $21.60   $21.60  
  Purchase #5 $48.40   8.787%   $52.6529   $52.65   $52.65   $52.70  
  Purchase #6 $152.63   12.195%   $171.2432   $171.24   $171.25   $171.20  
  Purchase #7 $184.76   10.113%   $203.4448   $203.44   $203.45   $203.40  
  7 purchase totals = $800.89       $879.0303   $879.02   $879.05   $879.00