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 $193.41   10.266%   $213.2655   $213.27   $213.25   $213.30  
  Purchase #2 $180.30   13.506%   $204.6513   $204.65   $204.65   $204.70  
  Purchase #3 $245.42   11.703%   $274.1415   $274.14   $274.15   $274.10  
  Purchase #4 $224.69   4.345%   $234.4528   $234.45   $234.45   $234.50  
  Purchase #5 $240.54   4.627%   $251.6698   $251.67   $251.65   $251.70  
  Purchase #6 $65.52   3.737%   $67.9685   $67.97   $67.95   $68.00  
  Purchase #7 $179.98   4.684%   $188.4103   $188.41   $188.40   $188.40  
  7 purchase totals = $1,329.86       $1,434.5597   $1,434.56   $1,434.50   $1,434.70