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 $226.29   12.541%   $254.669   $254.67   $254.65   $254.70  
  Purchase #2 $79.68   4.393%   $83.1803   $83.18   $83.20   $83.20  
  Purchase #3 $81.39   12.867%   $91.8625   $91.86   $91.85   $91.90  
  Purchase #4 $149.71   9.622%   $164.1151   $164.12   $164.10   $164.10  
  Purchase #5 $144.70   6.171%   $153.6294   $153.63   $153.65   $153.60  
  Purchase #6 $82.40   5.623%   $87.0334   $87.03   $87.05   $87.00  
  Purchase #7 $168.53   4.418%   $175.9757   $175.98   $176.00   $176.00  
  7 purchase totals = $932.70       $1,010.4654   $1,010.47   $1,010.50   $1,010.50