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 $235.51   12.503%   $264.9558   $264.96   $264.95   $265.00  
  Purchase #2 $193.47   6.688%   $206.4093   $206.41   $206.40   $206.40  
  Purchase #3 $11.65   8.660%   $12.6589   $12.66   $12.65   $12.70  
  Purchase #4 $112.77   8.443%   $122.2912   $122.29   $122.30   $122.30  
  Purchase #5 $23.95   4.687%   $25.0725   $25.07   $25.05   $25.10  
  Purchase #6 $92.65   12.293%   $104.0395   $104.04   $104.05   $104.00  
  Purchase #7 $166.85   5.257%   $175.6213   $175.62   $175.60   $175.60  
  7 purchase totals = $836.85       $911.0485   $911.05   $911.00   $911.10