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 $92.41   13.771%   $105.1358   $105.14   $105.15   $105.10  
  Purchase #2 $179.95   8.117%   $194.5565   $194.56   $194.55   $194.60  
  Purchase #3 $126.82   6.508%   $135.0734   $135.07   $135.05   $135.10  
  Purchase #4 $161.31   6.430%   $171.6822   $171.68   $171.70   $171.70  
  Purchase #5 $75.60   5.562%   $79.8049   $79.80   $79.80   $79.80  
  Purchase #6 $115.65   3.690%   $119.9175   $119.92   $119.90   $119.90  
  Purchase #7 $201.27   4.117%   $209.5563   $209.56   $209.55   $209.60  
  7 purchase totals = $953.01       $1,015.7266   $1,015.73   $1,015.70   $1,015.80