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 $61.32   9.328%   $67.0399   $67.04   $67.05   $67.00  
  Purchase #2 $161.93   3.790%   $168.0671   $168.07   $168.05   $168.10  
  Purchase #3 $69.37   7.738%   $74.7379   $74.74   $74.75   $74.70  
  Purchase #4 $220.63   11.223%   $245.3913   $245.39   $245.40   $245.40  
  Purchase #5 $33.57   12.663%   $37.821   $37.82   $37.80   $37.80  
  Purchase #6 $108.99   10.453%   $120.3827   $120.38   $120.40   $120.40  
  Purchase #7 $138.68   6.513%   $147.7122   $147.71   $147.70   $147.70  
  7 purchase totals = $794.49       $861.1521   $861.15   $861.15   $861.10