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 $56.46   12.616%   $63.583   $63.58   $63.60   $63.60  
  Purchase #2 $108.36   9.329%   $118.4689   $118.47   $118.45   $118.50  
  Purchase #3 $124.46   8.835%   $135.456   $135.46   $135.45   $135.50  
  Purchase #4 $35.39   13.631%   $40.214   $40.21   $40.20   $40.20  
  Purchase #5 $222.41   11.266%   $247.4667   $247.47   $247.45   $247.50  
  Purchase #6 $139.80   6.418%   $148.7724   $148.77   $148.75   $148.80  
  Purchase #7 $214.33   12.317%   $240.729   $240.73   $240.75   $240.70  
  7 purchase totals = $901.21       $994.6900   $994.69   $994.65   $994.80