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 $53.85   3.243%   $55.5964   $55.60   $55.60   $55.60  
  Purchase #2 $177.89   7.365%   $190.9916   $190.99   $191.00   $191.00  
  Purchase #3 $58.97   5.570%   $62.2546   $62.25   $62.25   $62.30  
  Purchase #4 $231.67   4.537%   $242.1809   $242.18   $242.20   $242.20  
  Purchase #5 $67.41   5.833%   $71.342   $71.34   $71.35   $71.30  
  Purchase #6 $88.27   6.828%   $94.2971   $94.30   $94.30   $94.30  
  Purchase #7 $74.54   3.751%   $77.336   $77.34   $77.35   $77.30  
  7 purchase totals = $752.60       $793.9986   $794.00   $794.05   $794.00