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 $53.77   3.668%   $55.7423   $55.74   $55.75   $55.70  
  Purchase #2 $112.59   11.686%   $125.7473   $125.75   $125.75   $125.70  
  Purchase #3 $238.34   10.370%   $263.0559   $263.06   $263.05   $263.10  
  Purchase #4 $5.91   9.138%   $6.4501   $6.45   $6.45   $6.50  
  Purchase #5 $41.53   5.565%   $43.8411   $43.84   $43.85   $43.80  
  Purchase #6 $56.77   11.306%   $63.1884   $63.19   $63.20   $63.20  
  Purchase #7 $212.94   9.418%   $232.9947   $232.99   $233.00   $233.00  
  7 purchase totals = $721.85       $791.0198   $791.02   $791.05   $791.00