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 $95.66   9.474%   $104.7228   $104.72   $104.70   $104.70  
  Purchase #2 $8.73   7.256%   $9.3634   $9.36   $9.35   $9.40  
  Purchase #3 $71.92   11.581%   $80.2491   $80.25   $80.25   $80.20  
  Purchase #4 $222.61   6.444%   $236.955   $236.96   $236.95   $237.00  
  Purchase #5 $208.68   11.179%   $232.0083   $232.01   $232.00   $232.00  
  Purchase #6 $105.74   10.526%   $116.8702   $116.87   $116.85   $116.90  
  Purchase #7 $22.90   7.375%   $24.5889   $24.59   $24.60   $24.60  
  7 purchase totals = $736.24       $804.7577   $804.76   $804.70   $804.80