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 $124.65   3.493%   $129.004   $129.00   $129.00   $129.00  
  Purchase #2 $108.67   10.130%   $119.6783   $119.68   $119.70   $119.70  
  Purchase #3 $69.48   13.299%   $78.7201   $78.72   $78.70   $78.70  
  Purchase #4 $168.95   4.477%   $176.5139   $176.51   $176.50   $176.50  
  Purchase #5 $116.54   6.405%   $124.0044   $124.00   $124.00   $124.00  
  Purchase #6 $204.98   9.210%   $223.8587   $223.86   $223.85   $223.90  
  Purchase #7 $69.94   7.272%   $75.026   $75.03   $75.05   $75.00  
  7 purchase totals = $863.21       $926.8054   $926.80   $926.80   $926.80