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 $26.92   11.859%   $30.1124   $30.11   $30.10   $30.10  
  Purchase #2 $112.58   3.797%   $116.8547   $116.85   $116.85   $116.90  
  Purchase #3 $179.45   12.320%   $201.5582   $201.56   $201.55   $201.60  
  Purchase #4 $243.66   9.817%   $267.5801   $267.58   $267.60   $267.60  
  Purchase #5 $101.87   9.109%   $111.1493   $111.15   $111.15   $111.10  
  Purchase #6 $6.83   5.199%   $7.1851   $7.19   $7.20   $7.20  
  Purchase #7 $23.47   6.407%   $24.9737   $24.97   $24.95   $25.00  
  7 purchase totals = $694.78       $759.4135   $759.41   $759.40   $759.50