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 $13.34   6.433%   $14.1982   $14.20   $14.20   $14.20  
  Purchase #2 $53.78   9.627%   $58.9574   $58.96   $58.95   $59.00  
  Purchase #3 $247.33   12.141%   $277.3583   $277.36   $277.35   $277.40  
  Purchase #4 $184.99   11.310%   $205.9124   $205.91   $205.90   $205.90  
  Purchase #5 $227.50   9.637%   $249.4242   $249.42   $249.40   $249.40  
  Purchase #6 $101.66   4.281%   $106.0121   $106.01   $106.00   $106.00  
  Purchase #7 $81.43   4.864%   $85.3908   $85.39   $85.40   $85.40  
  7 purchase totals = $910.03       $997.2534   $997.25   $997.20   $997.30