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 $184.61   3.837%   $191.6935   $191.69   $191.70   $191.70  
  Purchase #2 $94.63   11.697%   $105.6989   $105.70   $105.70   $105.70  
  Purchase #3 $40.58   11.856%   $45.3912   $45.39   $45.40   $45.40  
  Purchase #4 $74.31   3.226%   $76.7072   $76.71   $76.70   $76.70  
  Purchase #5 $225.84   3.131%   $232.9111   $232.91   $232.90   $232.90  
  Purchase #6 $47.56   9.292%   $51.9793   $51.98   $52.00   $52.00  
  Purchase #7 $131.40   10.853%   $145.6608   $145.66   $145.65   $145.70  
  7 purchase totals = $798.93       $850.0420   $850.04   $850.05   $850.10