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 $46.89   13.107%   $53.0359   $53.04   $53.05   $53.00  
  Purchase #2 $224.39   5.451%   $236.6215   $236.62   $236.60   $236.60  
  Purchase #3 $95.66   6.415%   $101.7966   $101.80   $101.80   $101.80  
  Purchase #4 $76.98   3.429%   $79.6196   $79.62   $79.60   $79.60  
  Purchase #5 $124.45   11.629%   $138.9223   $138.92   $138.90   $138.90  
  Purchase #6 $177.82   8.391%   $192.7409   $192.74   $192.75   $192.70  
  Purchase #7 $203.31   12.762%   $229.2564   $229.26   $229.25   $229.30  
  7 purchase totals = $949.50       $1,031.9932   $1,032.00   $1,031.95   $1,031.90