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 $193.72   13.361%   $219.6029   $219.60   $219.60   $219.60  
  Purchase #2 $192.95   7.415%   $207.2572   $207.26   $207.25   $207.30  
  Purchase #3 $32.51   11.793%   $36.3439   $36.34   $36.35   $36.30  
  Purchase #4 $191.43   3.290%   $197.728   $197.73   $197.75   $197.70  
  Purchase #5 $210.95   13.338%   $239.0865   $239.09   $239.10   $239.10  
  Purchase #6 $229.50   8.800%   $249.696   $249.70   $249.70   $249.70  
  Purchase #7 $197.78   7.192%   $212.0043   $212.00   $212.00   $212.00  
  7 purchase totals = $1,248.84       $1,361.7188   $1,361.72   $1,361.75   $1,361.70