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 $94.68   8.852%   $103.0611   $103.06   $103.05   $103.10  
  Purchase #2 $23.29   11.136%   $25.8836   $25.88   $25.90   $25.90  
  Purchase #3 $110.93   8.722%   $120.6053   $120.61   $120.60   $120.60  
  Purchase #4 $208.45   9.142%   $227.5065   $227.51   $227.50   $227.50  
  Purchase #5 $81.29   4.361%   $84.8351   $84.84   $84.85   $84.80  
  Purchase #6 $205.38   11.851%   $229.7196   $229.72   $229.70   $229.70  
  Purchase #7 $134.97   7.447%   $145.0212   $145.02   $145.00   $145.00  
  7 purchase totals = $858.99       $936.6324   $936.64   $936.60   $936.60