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 $62.37   10.429%   $68.8746   $68.87   $68.85   $68.90  
  Purchase #2 $205.68   13.540%   $233.5291   $233.53   $233.55   $233.50  
  Purchase #3 $210.85   5.253%   $221.926   $221.93   $221.95   $221.90  
  Purchase #4 $121.87   8.167%   $131.8231   $131.82   $131.80   $131.80  
  Purchase #5 $52.99   7.527%   $56.9786   $56.98   $57.00   $57.00  
  Purchase #6 $88.59   9.804%   $97.2754   $97.28   $97.30   $97.30  
  Purchase #7 $57.91   8.239%   $62.6812   $62.68   $62.70   $62.70  
  7 purchase totals = $800.26       $873.0880   $873.09   $873.15   $873.10