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 $246.58   7.809%   $265.8354   $265.84   $265.85   $265.80  
  Purchase #2 $68.65   13.401%   $77.8498   $77.85   $77.85   $77.80  
  Purchase #3 $191.75   13.516%   $217.6669   $217.67   $217.65   $217.70  
  Purchase #4 $226.36   9.695%   $248.3056   $248.31   $248.30   $248.30  
  Purchase #5 $210.55   3.514%   $217.9487   $217.95   $217.95   $217.90  
  Purchase #6 $148.92   7.722%   $160.4196   $160.42   $160.40   $160.40  
  Purchase #7 $234.38   11.337%   $260.9517   $260.95   $260.95   $261.00  
  7 purchase totals = $1,327.19       $1,448.9777   $1,448.99   $1,448.95   $1,448.90