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 $228.30   13.505%   $259.1319   $259.13   $259.15   $259.10  
  Purchase #2 $212.87   11.621%   $237.6076   $237.61   $237.60   $237.60  
  Purchase #3 $70.84   5.480%   $74.722   $74.72   $74.70   $74.70  
  Purchase #4 $216.40   3.677%   $224.357   $224.36   $224.35   $224.40  
  Purchase #5 $54.27   12.342%   $60.968   $60.97   $60.95   $61.00  
  Purchase #6 $210.87   11.522%   $235.1664   $235.17   $235.15   $235.20  
  Purchase #7 $137.69   3.702%   $142.7873   $142.79   $142.80   $142.80  
  7 purchase totals = $1,131.24       $1,234.7402   $1,234.75   $1,234.70   $1,234.80