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 $202.82   13.721%   $230.6489   $230.65   $230.65   $230.60  
  Purchase #2 $41.33   11.298%   $45.9995   $46.00   $46.00   $46.00  
  Purchase #3 $233.90   6.823%   $249.859   $249.86   $249.85   $249.90  
  Purchase #4 $216.68   8.475%   $235.0436   $235.04   $235.05   $235.00  
  Purchase #5 $124.89   5.616%   $131.9038   $131.90   $131.90   $131.90  
  Purchase #6 $150.78   10.119%   $166.0374   $166.04   $166.05   $166.00  
  Purchase #7 $240.85   13.766%   $274.0054   $274.01   $274.00   $274.00  
  7 purchase totals = $1,211.25       $1,333.4976   $1,333.50   $1,333.50   $1,333.40