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 $22.44   10.542%   $24.8056   $24.81   $24.80   $24.80  
  Purchase #2 $188.31   11.268%   $209.5288   $209.53   $209.55   $209.50  
  Purchase #3 $72.49   7.482%   $77.9137   $77.91   $77.90   $77.90  
  Purchase #4 $207.81   12.741%   $234.2871   $234.29   $234.30   $234.30  
  Purchase #5 $102.51   10.627%   $113.4037   $113.40   $113.40   $113.40  
  Purchase #6 $159.46   9.820%   $175.119   $175.12   $175.10   $175.10  
  Purchase #7 $211.57   12.279%   $237.5487   $237.55   $237.55   $237.50  
  7 purchase totals = $964.59       $1,072.6066   $1,072.61   $1,072.60   $1,072.50