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 $97.53   6.493%   $103.8626   $103.86   $103.85   $103.90  
  Purchase #2 $22.36   8.579%   $24.2783   $24.28   $24.30   $24.30  
  Purchase #3 $152.85   8.465%   $165.7888   $165.79   $165.80   $165.80  
  Purchase #4 $87.55   8.669%   $95.1397   $95.14   $95.15   $95.10  
  Purchase #5 $62.55   12.696%   $70.4913   $70.49   $70.50   $70.50  
  Purchase #6 $41.46   8.824%   $45.1184   $45.12   $45.10   $45.10  
  Purchase #7 $233.29   13.596%   $265.0081   $265.01   $265.00   $265.00  
  7 purchase totals = $697.59       $769.6872   $769.69   $769.70   $769.70