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 $60.46   13.561%   $68.659   $68.66   $68.65   $68.70  
  Purchase #2 $129.91   6.609%   $138.4958   $138.50   $138.50   $138.50  
  Purchase #3 $53.68   13.375%   $60.8597   $60.86   $60.85   $60.90  
  Purchase #4 $60.33   9.644%   $66.1482   $66.15   $66.15   $66.10  
  Purchase #5 $191.90   9.583%   $210.2898   $210.29   $210.30   $210.30  
  Purchase #6 $115.70   4.138%   $120.4877   $120.49   $120.50   $120.50  
  Purchase #7 $233.69   12.181%   $262.1558   $262.16   $262.15   $262.20  
  7 purchase totals = $845.67       $927.0960   $927.11   $927.10   $927.20