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 $54.52   10.382%   $60.1803   $60.18   $60.20   $60.20  
  Purchase #2 $106.98   4.733%   $112.0434   $112.04   $112.05   $112.00  
  Purchase #3 $6.40   7.498%   $6.8799   $6.88   $6.90   $6.90  
  Purchase #4 $160.95   13.734%   $183.0549   $183.05   $183.05   $183.10  
  Purchase #5 $139.52   9.812%   $153.2097   $153.21   $153.20   $153.20  
  Purchase #6 $67.80   3.547%   $70.2049   $70.20   $70.20   $70.20  
  Purchase #7 $250.84   7.325%   $269.214   $269.21   $269.20   $269.20  
  7 purchase totals = $787.01       $854.7871   $854.77   $854.80   $854.80