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 $71.33   8.225%   $77.1969   $77.20   $77.20   $77.20  
  Purchase #2 $101.62   11.564%   $113.3713   $113.37   $113.35   $113.40  
  Purchase #3 $8.47   10.754%   $9.3809   $9.38   $9.40   $9.40  
  Purchase #4 $200.62   4.812%   $210.2738   $210.27   $210.25   $210.30  
  Purchase #5 $41.85   6.632%   $44.6255   $44.63   $44.65   $44.60  
  Purchase #6 $174.50   3.313%   $180.2812   $180.28   $180.30   $180.30  
  Purchase #7 $115.80   5.387%   $122.0381   $122.04   $122.05   $122.00  
  7 purchase totals = $714.19       $757.1677   $757.17   $757.20   $757.20