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 $60.63   6.821%   $64.7656   $64.77   $64.75   $64.80  
  Purchase #2 $60.71   3.849%   $63.0467   $63.05   $63.05   $63.00  
  Purchase #3 $140.76   11.438%   $156.8601   $156.86   $156.85   $156.90  
  Purchase #4 $29.80   9.665%   $32.6802   $32.68   $32.70   $32.70  
  Purchase #5 $110.85   10.234%   $122.1944   $122.19   $122.20   $122.20  
  Purchase #6 $190.79   7.819%   $205.7079   $205.71   $205.70   $205.70  
  Purchase #7 $201.57   5.678%   $213.0151   $213.02   $213.00   $213.00  
  7 purchase totals = $795.11       $858.2700   $858.28   $858.25   $858.30