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 $148.70   9.834%   $163.3232   $163.32   $163.30   $163.30  
  Purchase #2 $221.56   9.817%   $243.3105   $243.31   $243.30   $243.30  
  Purchase #3 $73.33   3.602%   $75.9713   $75.97   $75.95   $76.00  
  Purchase #4 $215.77   5.715%   $228.1013   $228.10   $228.10   $228.10  
  Purchase #5 $215.93   7.839%   $232.8568   $232.86   $232.85   $232.90  
  Purchase #6 $167.78   10.779%   $185.865   $185.87   $185.85   $185.90  
  Purchase #7 $117.86   7.851%   $127.1132   $127.11   $127.10   $127.10  
  7 purchase totals = $1,160.93       $1,256.5413   $1,256.54   $1,256.45   $1,256.60