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 $41.75   11.760%   $46.6598   $46.66   $46.65   $46.70  
  Purchase #2 $211.91   12.610%   $238.6319   $238.63   $238.65   $238.60  
  Purchase #3 $93.59   12.859%   $105.6247   $105.62   $105.60   $105.60  
  Purchase #4 $127.71   6.849%   $136.4569   $136.46   $136.45   $136.50  
  Purchase #5 $113.29   6.517%   $120.6731   $120.67   $120.65   $120.70  
  Purchase #6 $19.33   6.623%   $20.6102   $20.61   $20.60   $20.60  
  Purchase #7 $87.29   4.392%   $91.1238   $91.12   $91.10   $91.10  
  7 purchase totals = $694.87       $759.7804   $759.77   $759.70   $759.80