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 $95.45   12.451%   $107.3345   $107.33   $107.35   $107.30  
  Purchase #2 $66.82   3.122%   $68.9061   $68.91   $68.90   $68.90  
  Purchase #3 $180.90   11.180%   $201.1246   $201.12   $201.10   $201.10  
  Purchase #4 $157.34   11.411%   $175.2941   $175.29   $175.30   $175.30  
  Purchase #5 $240.46   6.425%   $255.9096   $255.91   $255.90   $255.90  
  Purchase #6 $201.80   3.796%   $209.4603   $209.46   $209.45   $209.50  
  Purchase #7 $214.97   4.786%   $225.2585   $225.26   $225.25   $225.30  
  7 purchase totals = $1,157.74       $1,243.2877   $1,243.28   $1,243.25   $1,243.30