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 $204.99   11.728%   $229.0312   $229.03   $229.05   $229.00  
  Purchase #2 $70.80   7.664%   $76.2261   $76.23   $76.25   $76.20  
  Purchase #3 $89.32   10.245%   $98.4708   $98.47   $98.45   $98.50  
  Purchase #4 $210.44   7.263%   $225.7243   $225.72   $225.70   $225.70  
  Purchase #5 $95.85   13.649%   $108.9326   $108.93   $108.95   $108.90  
  Purchase #6 $159.67   8.764%   $173.6635   $173.66   $173.65   $173.70  
  Purchase #7 $160.57   8.337%   $173.9567   $173.96   $173.95   $174.00  
  7 purchase totals = $991.64       $1,086.0052   $1,086.00   $1,086.00   $1,086.00