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 $239.58   3.260%   $247.3903   $247.39   $247.40   $247.40  
  Purchase #2 $216.96   3.186%   $223.8723   $223.87   $223.85   $223.90  
  Purchase #3 $53.27   13.653%   $60.543   $60.54   $60.55   $60.50  
  Purchase #4 $85.72   11.817%   $95.8495   $95.85   $95.85   $95.80  
  Purchase #5 $77.61   13.540%   $88.1184   $88.12   $88.10   $88.10  
  Purchase #6 $183.78   4.303%   $191.6881   $191.69   $191.70   $191.70  
  Purchase #7 $216.42   5.569%   $228.4724   $228.47   $228.45   $228.50  
  7 purchase totals = $1,073.34       $1,135.9340   $1,135.93   $1,135.90   $1,135.90