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 $23.68   13.631%   $26.9078   $26.91   $26.90   $26.90  
  Purchase #2 $89.39   6.398%   $95.1092   $95.11   $95.10   $95.10  
  Purchase #3 $98.40   11.113%   $109.3352   $109.34   $109.35   $109.30  
  Purchase #4 $57.46   13.309%   $65.1074   $65.11   $65.10   $65.10  
  Purchase #5 $202.27   3.363%   $209.0723   $209.07   $209.05   $209.10  
  Purchase #6 $231.99   7.303%   $248.9322   $248.93   $248.95   $248.90  
  Purchase #7 $35.87   11.534%   $40.0072   $40.01   $40.00   $40.00  
  7 purchase totals = $739.06       $794.4713   $794.48   $794.45   $794.40