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 $61.36   5.229%   $64.5685   $64.57   $64.55   $64.60  
  Purchase #2 $181.97   9.614%   $199.4646   $199.46   $199.45   $199.50  
  Purchase #3 $21.92   13.119%   $24.7957   $24.80   $24.80   $24.80  
  Purchase #4 $181.28   13.283%   $205.3594   $205.36   $205.35   $205.40  
  Purchase #5 $36.97   4.215%   $38.5283   $38.53   $38.55   $38.50  
  Purchase #6 $117.76   8.722%   $128.031   $128.03   $128.05   $128.00  
  Purchase #7 $175.92   13.681%   $199.9876   $199.99   $200.00   $200.00  
  7 purchase totals = $777.18       $860.7351   $860.74   $860.75   $860.80