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 $213.93   9.494%   $234.2405   $234.24   $234.25   $234.20  
  Purchase #2 $55.95   5.132%   $58.8214   $58.82   $58.80   $58.80  
  Purchase #3 $237.78   6.573%   $253.4093   $253.41   $253.40   $253.40  
  Purchase #4 $68.27   11.228%   $75.9354   $75.94   $75.95   $75.90  
  Purchase #5 $131.57   8.394%   $142.614   $142.61   $142.60   $142.60  
  Purchase #6 $204.90   13.331%   $232.2152   $232.22   $232.20   $232.20  
  Purchase #7 $126.90   12.412%   $142.6508   $142.65   $142.65   $142.70  
  7 purchase totals = $1,039.30       $1,139.8866   $1,139.89   $1,139.85   $1,139.80