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 $46.52   6.584%   $49.5829   $49.58   $49.60   $49.60  
  Purchase #2 $78.27   11.220%   $87.0519   $87.05   $87.05   $87.10  
  Purchase #3 $151.71   5.295%   $159.743   $159.74   $159.75   $159.70  
  Purchase #4 $65.94   5.293%   $69.4302   $69.43   $69.45   $69.40  
  Purchase #5 $192.69   12.548%   $216.8687   $216.87   $216.85   $216.90  
  Purchase #6 $83.90   13.301%   $95.0595   $95.06   $95.05   $95.10  
  Purchase #7 $229.89   6.650%   $245.1777   $245.18   $245.20   $245.20  
  7 purchase totals = $848.92       $922.9139   $922.91   $922.95   $923.00