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 $240.72   10.380%   $265.7067   $265.71   $265.70   $265.70  
  Purchase #2 $6.49   4.368%   $6.7735   $6.77   $6.75   $6.80  
  Purchase #3 $106.25   6.669%   $113.3358   $113.34   $113.35   $113.30  
  Purchase #4 $173.27   3.547%   $179.4159   $179.42   $179.40   $179.40  
  Purchase #5 $125.40   8.667%   $136.2684   $136.27   $136.25   $136.30  
  Purchase #6 $19.36   3.429%   $20.0239   $20.02   $20.00   $20.00  
  Purchase #7 $214.47   6.760%   $228.9682   $228.97   $228.95   $229.00  
  7 purchase totals = $885.96       $950.4924   $950.50   $950.40   $950.50