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 $52.81   5.145%   $55.5271   $55.53   $55.55   $55.50  
  Purchase #2 $90.43   8.695%   $98.2929   $98.29   $98.30   $98.30  
  Purchase #3 $209.70   12.533%   $235.9817   $235.98   $236.00   $236.00  
  Purchase #4 $146.76   8.714%   $159.5487   $159.55   $159.55   $159.50  
  Purchase #5 $246.31   5.465%   $259.7708   $259.77   $259.75   $259.80  
  Purchase #6 $214.31   5.571%   $226.2492   $226.25   $226.25   $226.20  
  Purchase #7 $20.43   12.592%   $23.0025   $23.00   $23.00   $23.00  
  7 purchase totals = $980.75       $1,058.3729   $1,058.37   $1,058.40   $1,058.30