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 $58.51   11.172%   $65.0467   $65.05   $65.05   $65.00  
  Purchase #2 $216.64   8.687%   $235.4595   $235.46   $235.45   $235.50  
  Purchase #3 $235.53   4.378%   $245.8415   $245.84   $245.85   $245.80  
  Purchase #4 $243.67   8.669%   $264.7938   $264.79   $264.80   $264.80  
  Purchase #5 $192.98   12.872%   $217.8204   $217.82   $217.80   $217.80  
  Purchase #6 $6.71   11.299%   $7.4682   $7.47   $7.45   $7.50  
  Purchase #7 $225.34   10.801%   $249.679   $249.68   $249.70   $249.70  
  7 purchase totals = $1,179.38       $1,286.1091   $1,286.11   $1,286.10   $1,286.10