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 $213.53   6.787%   $228.0223   $228.02   $228.00   $228.00  
  Purchase #2 $134.61   12.565%   $151.5237   $151.52   $151.50   $151.50  
  Purchase #3 $155.34   9.429%   $169.987   $169.99   $170.00   $170.00  
  Purchase #4 $205.57   7.681%   $221.3598   $221.36   $221.35   $221.40  
  Purchase #5 $213.64   6.212%   $226.9113   $226.91   $226.90   $226.90  
  Purchase #6 $169.83   5.486%   $179.1469   $179.15   $179.15   $179.10  
  Purchase #7 $71.88   4.394%   $75.0384   $75.04   $75.05   $75.00  
  7 purchase totals = $1,164.40       $1,251.9894   $1,251.99   $1,251.95   $1,251.90