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 $218.53   10.584%   $241.6592   $241.66   $241.65   $241.70  
  Purchase #2 $71.51   5.812%   $75.6662   $75.67   $75.65   $75.70  
  Purchase #3 $37.45   4.265%   $39.0472   $39.05   $39.05   $39.00  
  Purchase #4 $61.91   8.371%   $67.0925   $67.09   $67.10   $67.10  
  Purchase #5 $44.56   10.135%   $49.0762   $49.08   $49.10   $49.10  
  Purchase #6 $229.48   13.795%   $261.1368   $261.14   $261.15   $261.10  
  Purchase #7 $34.28   8.208%   $37.0937   $37.09   $37.10   $37.10  
  7 purchase totals = $697.72       $770.7718   $770.78   $770.80   $770.80