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 $210.59   11.271%   $234.3256   $234.33   $234.35   $234.30  
  Purchase #2 $84.38   10.238%   $93.0188   $93.02   $93.00   $93.00  
  Purchase #3 $149.25   8.179%   $161.4572   $161.46   $161.45   $161.50  
  Purchase #4 $11.56   8.553%   $12.5487   $12.55   $12.55   $12.50  
  Purchase #5 $51.34   5.843%   $54.3398   $54.34   $54.35   $54.30  
  Purchase #6 $224.52   12.455%   $252.484   $252.48   $252.50   $252.50  
  Purchase #7 $107.58   3.283%   $111.1119   $111.11   $111.10   $111.10  
  7 purchase totals = $839.22       $919.2860   $919.29   $919.30   $919.20