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 $65.58   13.171%   $74.2175   $74.22   $74.20   $74.20  
  Purchase #2 $230.26   4.297%   $240.1543   $240.15   $240.15   $240.20  
  Purchase #3 $134.38   11.243%   $149.4883   $149.49   $149.50   $149.50  
  Purchase #4 $43.36   7.670%   $46.6857   $46.69   $46.70   $46.70  
  Purchase #5 $93.36   4.160%   $97.2438   $97.24   $97.25   $97.20  
  Purchase #6 $120.25   9.737%   $131.9587   $131.96   $131.95   $132.00  
  Purchase #7 $26.94   11.690%   $30.0893   $30.09   $30.10   $30.10  
  7 purchase totals = $714.13       $769.8376   $769.84   $769.85   $769.90