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 $219.71   8.795%   $239.0335   $239.03   $239.05   $239.00  
  Purchase #2 $248.78   4.764%   $260.6319   $260.63   $260.65   $260.60  
  Purchase #3 $29.66   5.529%   $31.2999   $31.30   $31.30   $31.30  
  Purchase #4 $204.32   8.108%   $220.8863   $220.89   $220.90   $220.90  
  Purchase #5 $59.81   11.567%   $66.7282   $66.73   $66.75   $66.70  
  Purchase #6 $24.79   11.672%   $27.6835   $27.68   $27.70   $27.70  
  Purchase #7 $183.44   11.587%   $204.6952   $204.70   $204.70   $204.70  
  7 purchase totals = $970.51       $1,050.9585   $1,050.96   $1,051.05   $1,050.90