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 $31.73   10.371%   $35.0207   $35.02   $35.00   $35.00  
  Purchase #2 $106.79   11.431%   $118.9972   $119.00   $119.00   $119.00  
  Purchase #3 $127.64   10.129%   $140.5687   $140.57   $140.55   $140.60  
  Purchase #4 $16.87   3.767%   $17.5055   $17.51   $17.50   $17.50  
  Purchase #5 $211.55   10.152%   $233.0266   $233.03   $233.05   $233.00  
  Purchase #6 $128.91   13.601%   $146.443   $146.44   $146.45   $146.40  
  Purchase #7 $110.84   8.772%   $120.5629   $120.56   $120.55   $120.60  
  7 purchase totals = $734.33       $812.1246   $812.13   $812.10   $812.10