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 $51.99   13.409%   $58.9613   $58.96   $58.95   $59.00  
  Purchase #2 $160.56   5.671%   $169.6654   $169.67   $169.65   $169.70  
  Purchase #3 $89.90   5.430%   $94.7816   $94.78   $94.80   $94.80  
  Purchase #4 $19.26   5.536%   $20.3262   $20.33   $20.35   $20.30  
  Purchase #5 $19.48   12.250%   $21.8663   $21.87   $21.85   $21.90  
  Purchase #6 $184.86   3.832%   $191.9438   $191.94   $191.95   $191.90  
  Purchase #7 $37.93   3.659%   $39.3179   $39.32   $39.30   $39.30  
  7 purchase totals = $563.98       $596.8625   $596.87   $596.85   $596.90