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 $65.99   12.563%   $74.2803   $74.28   $74.30   $74.30  
  Purchase #2 $202.46   7.485%   $217.6141   $217.61   $217.60   $217.60  
  Purchase #3 $88.27   7.788%   $95.1445   $95.14   $95.15   $95.10  
  Purchase #4 $120.97   12.229%   $135.7634   $135.76   $135.75   $135.80  
  Purchase #5 $232.57   5.618%   $245.6358   $245.64   $245.65   $245.60  
  Purchase #6 $59.34   11.314%   $66.0537   $66.05   $66.05   $66.10  
  Purchase #7 $94.48   7.698%   $101.7531   $101.75   $101.75   $101.80  
  7 purchase totals = $864.08       $936.2449   $936.23   $936.25   $936.30