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 $136.35   9.336%   $149.0796   $149.08   $149.10   $149.10  
  Purchase #2 $150.32   6.142%   $159.5527   $159.55   $159.55   $159.60  
  Purchase #3 $169.98   13.445%   $192.8338   $192.83   $192.85   $192.80  
  Purchase #4 $187.29   4.139%   $195.0419   $195.04   $195.05   $195.00  
  Purchase #5 $43.66   13.508%   $49.5576   $49.56   $49.55   $49.60  
  Purchase #6 $202.69   3.824%   $210.4409   $210.44   $210.45   $210.40  
  Purchase #7 $61.66   8.403%   $66.8413   $66.84   $66.85   $66.80  
  7 purchase totals = $951.95       $1,023.3478   $1,023.34   $1,023.40   $1,023.30