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 $114.48   8.809%   $124.5645   $124.56   $124.55   $124.60  
  Purchase #2 $30.42   11.343%   $33.8705   $33.87   $33.85   $33.90  
  Purchase #3 $46.56   6.273%   $49.4807   $49.48   $49.50   $49.50  
  Purchase #4 $224.61   8.121%   $242.8506   $242.85   $242.85   $242.90  
  Purchase #5 $155.74   8.288%   $168.6477   $168.65   $168.65   $168.60  
  Purchase #6 $191.77   9.487%   $209.9632   $209.96   $209.95   $210.00  
  Purchase #7 $22.35   3.289%   $23.0851   $23.09   $23.10   $23.10  
  7 purchase totals = $785.93       $852.4623   $852.46   $852.45   $852.60