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 $22.94   12.567%   $25.8229   $25.82   $25.80   $25.80  
  Purchase #2 $112.47   5.494%   $118.6491   $118.65   $118.65   $118.60  
  Purchase #3 $250.37   3.589%   $259.3558   $259.36   $259.35   $259.40  
  Purchase #4 $153.31   11.429%   $170.8318   $170.83   $170.85   $170.80  
  Purchase #5 $151.78   12.550%   $170.8284   $170.83   $170.85   $170.80  
  Purchase #6 $149.33   4.785%   $156.4754   $156.48   $156.50   $156.50  
  Purchase #7 $147.37   12.552%   $165.8679   $165.87   $165.85   $165.90  
  7 purchase totals = $987.57       $1,067.8313   $1,067.84   $1,067.85   $1,067.80