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 $85.90   13.481%   $97.4802   $97.48   $97.50   $97.50  
  Purchase #2 $209.73   13.652%   $238.3623   $238.36   $238.35   $238.40  
  Purchase #3 $67.93   11.730%   $75.8982   $75.90   $75.90   $75.90  
  Purchase #4 $212.61   7.573%   $228.711   $228.71   $228.70   $228.70  
  Purchase #5 $111.92   5.546%   $118.1271   $118.13   $118.15   $118.10  
  Purchase #6 $75.59   3.224%   $78.027   $78.03   $78.05   $78.00  
  Purchase #7 $120.30   5.866%   $127.3568   $127.36   $127.35   $127.40  
  7 purchase totals = $883.98       $963.9626   $963.97   $964.00   $964.00