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 $205.72   11.610%   $229.6041   $229.60   $229.60   $229.60  
  Purchase #2 $100.58   6.665%   $107.2837   $107.28   $107.30   $107.30  
  Purchase #3 $140.92   5.191%   $148.2352   $148.24   $148.25   $148.20  
  Purchase #4 $118.69   10.177%   $130.7691   $130.77   $130.75   $130.80  
  Purchase #5 $139.78   8.246%   $151.3063   $151.31   $151.30   $151.30  
  Purchase #6 $25.55   13.802%   $29.0764   $29.08   $29.10   $29.10  
  Purchase #7 $235.92   11.757%   $263.6571   $263.66   $263.65   $263.70  
  7 purchase totals = $967.16       $1,059.9319   $1,059.94   $1,059.95   $1,060.00