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 $96.36   10.169%   $106.1588   $106.16   $106.15   $106.20  
  Purchase #2 $150.55   11.150%   $167.3363   $167.34   $167.35   $167.30  
  Purchase #3 $73.84   4.579%   $77.2211   $77.22   $77.20   $77.20  
  Purchase #4 $136.47   11.575%   $152.2664   $152.27   $152.25   $152.30  
  Purchase #5 $158.69   6.790%   $169.4651   $169.47   $169.45   $169.50  
  Purchase #6 $71.56   12.128%   $80.2388   $80.24   $80.25   $80.20  
  Purchase #7 $14.44   12.464%   $16.2398   $16.24   $16.25   $16.20  
  7 purchase totals = $701.91       $768.9263   $768.94   $768.90   $768.90