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 $61.55   5.855%   $65.1538   $65.15   $65.15   $65.20  
  Purchase #2 $53.86   12.650%   $60.6733   $60.67   $60.65   $60.70  
  Purchase #3 $239.49   11.632%   $267.3475   $267.35   $267.35   $267.30  
  Purchase #4 $39.54   12.548%   $44.5015   $44.50   $44.50   $44.50  
  Purchase #5 $203.91   12.309%   $229.0093   $229.01   $229.00   $229.00  
  Purchase #6 $48.79   8.361%   $52.8693   $52.87   $52.85   $52.90  
  Purchase #7 $68.96   3.673%   $71.4929   $71.49   $71.50   $71.50  
  7 purchase totals = $716.10       $791.0476   $791.04   $791.00   $791.10