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 $136.36   11.574%   $152.1423   $152.14   $152.15   $152.10  
  Purchase #2 $239.30   4.326%   $249.6521   $249.65   $249.65   $249.70  
  Purchase #3 $178.30   8.437%   $193.3432   $193.34   $193.35   $193.30  
  Purchase #4 $247.94   7.295%   $266.0272   $266.03   $266.05   $266.00  
  Purchase #5 $59.88   9.702%   $65.6896   $65.69   $65.70   $65.70  
  Purchase #6 $58.51   13.610%   $66.4732   $66.47   $66.45   $66.50  
  Purchase #7 $49.92   6.580%   $53.2047   $53.20   $53.20   $53.20  
  7 purchase totals = $970.21       $1,046.5323   $1,046.52   $1,046.55   $1,046.50