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 $90.49   5.291%   $95.2778   $95.28   $95.30   $95.30  
  Purchase #2 $73.76   13.279%   $83.5546   $83.55   $83.55   $83.60  
  Purchase #3 $61.88   13.119%   $69.998   $70.00   $70.00   $70.00  
  Purchase #4 $87.33   4.704%   $91.438   $91.44   $91.45   $91.40  
  Purchase #5 $160.47   12.186%   $180.0249   $180.02   $180.00   $180.00  
  Purchase #6 $123.88   6.546%   $131.9892   $131.99   $132.00   $132.00  
  Purchase #7 $92.47   5.717%   $97.7565   $97.76   $97.75   $97.80  
  7 purchase totals = $690.28       $750.0390   $750.04   $750.05   $750.10