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 $114.57   8.866%   $124.7278   $124.73   $124.75   $124.70  
  Purchase #2 $53.84   6.537%   $57.3595   $57.36   $57.35   $57.40  
  Purchase #3 $211.27   12.662%   $238.021   $238.02   $238.00   $238.00  
  Purchase #4 $34.55   6.700%   $36.8649   $36.86   $36.85   $36.90  
  Purchase #5 $95.64   9.247%   $104.4838   $104.48   $104.50   $104.50  
  Purchase #6 $112.55   3.658%   $116.6671   $116.67   $116.65   $116.70  
  Purchase #7 $245.57   9.855%   $269.7709   $269.77   $269.75   $269.80  
  7 purchase totals = $867.99       $947.8950   $947.89   $947.85   $948.00