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 $186.67   8.486%   $202.5108   $202.51   $202.50   $202.50  
  Purchase #2 $169.27   13.473%   $192.0757   $192.08   $192.10   $192.10  
  Purchase #3 $217.94   3.602%   $225.7902   $225.79   $225.80   $225.80  
  Purchase #4 $111.66   12.550%   $125.6733   $125.67   $125.65   $125.70  
  Purchase #5 $179.38   7.653%   $193.108   $193.11   $193.10   $193.10  
  Purchase #6 $202.37   9.163%   $220.9132   $220.91   $220.90   $220.90  
  Purchase #7 $100.25   8.668%   $108.9397   $108.94   $108.95   $108.90  
  7 purchase totals = $1,167.54       $1,269.0109   $1,269.01   $1,269.00   $1,269.00