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 $180.39   8.806%   $196.2751   $196.28   $196.30   $196.30  
  Purchase #2 $69.79   7.616%   $75.1052   $75.11   $75.10   $75.10  
  Purchase #3 $116.51   8.151%   $126.0067   $126.01   $126.00   $126.00  
  Purchase #4 $60.99   12.410%   $68.5589   $68.56   $68.55   $68.60  
  Purchase #5 $187.68   3.820%   $194.8494   $194.85   $194.85   $194.80  
  Purchase #6 $244.50   9.177%   $266.9378   $266.94   $266.95   $266.90  
  Purchase #7 $190.49   7.716%   $205.1882   $205.19   $205.20   $205.20  
  7 purchase totals = $1,050.35       $1,132.9213   $1,132.94   $1,132.95   $1,132.90