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 $203.71   13.279%   $230.7607   $230.76   $230.75   $230.80  
  Purchase #2 $173.54   12.285%   $194.8594   $194.86   $194.85   $194.90  
  Purchase #3 $75.73   5.456%   $79.8618   $79.86   $79.85   $79.90  
  Purchase #4 $48.99   3.221%   $50.568   $50.57   $50.55   $50.60  
  Purchase #5 $41.71   9.811%   $45.8022   $45.80   $45.80   $45.80  
  Purchase #6 $155.87   9.315%   $170.3893   $170.39   $170.40   $170.40  
  Purchase #7 $32.54   4.796%   $34.1006   $34.10   $34.10   $34.10  
  7 purchase totals = $732.09       $806.3420   $806.34   $806.30   $806.50