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 $249.26   5.370%   $262.6453   $262.65   $262.65   $262.60  
  Purchase #2 $163.88   13.643%   $186.2381   $186.24   $186.25   $186.20  
  Purchase #3 $89.46   9.348%   $97.8227   $97.82   $97.80   $97.80  
  Purchase #4 $174.92   13.393%   $198.347   $198.35   $198.35   $198.30  
  Purchase #5 $233.65   3.224%   $241.1829   $241.18   $241.20   $241.20  
  Purchase #6 $127.90   3.204%   $131.9979   $132.00   $132.00   $132.00  
  Purchase #7 $215.39   8.197%   $233.0455   $233.05   $233.05   $233.00  
  7 purchase totals = $1,254.46       $1,351.2794   $1,351.29   $1,351.30   $1,351.10