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 $225.75   11.563%   $251.8535   $251.85   $251.85   $251.90  
  Purchase #2 $101.73   8.827%   $110.7097   $110.71   $110.70   $110.70  
  Purchase #3 $65.39   6.543%   $69.6685   $69.67   $69.65   $69.70  
  Purchase #4 $56.56   3.837%   $58.7302   $58.73   $58.75   $58.70  
  Purchase #5 $82.62   5.625%   $87.2674   $87.27   $87.25   $87.30  
  Purchase #6 $47.87   10.471%   $52.8825   $52.88   $52.90   $52.90  
  Purchase #7 $245.92   7.676%   $264.7968   $264.80   $264.80   $264.80  
  7 purchase totals = $825.84       $895.9086   $895.91   $895.90   $896.00