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 $201.94   6.799%   $215.6699   $215.67   $215.65   $215.70  
  Purchase #2 $216.94   3.260%   $224.0122   $224.01   $224.00   $224.00  
  Purchase #3 $110.51   8.811%   $120.247   $120.25   $120.25   $120.20  
  Purchase #4 $209.79   4.488%   $219.2054   $219.21   $219.20   $219.20  
  Purchase #5 $155.92   6.189%   $165.5699   $165.57   $165.55   $165.60  
  Purchase #6 $162.61   8.656%   $176.6855   $176.69   $176.70   $176.70  
  Purchase #7 $187.90   4.214%   $195.8181   $195.82   $195.80   $195.80  
  7 purchase totals = $1,245.61       $1,317.2080   $1,317.22   $1,317.15   $1,317.20