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 $219.85   12.336%   $246.9707   $246.97   $246.95   $247.00  
  Purchase #2 $115.41   10.397%   $127.4092   $127.41   $127.40   $127.40  
  Purchase #3 $108.67   4.829%   $113.9177   $113.92   $113.90   $113.90  
  Purchase #4 $12.73   11.508%   $14.195   $14.20   $14.20   $14.20  
  Purchase #5 $151.89   6.723%   $162.1016   $162.10   $162.10   $162.10  
  Purchase #6 $197.48   10.817%   $218.8414   $218.84   $218.85   $218.80  
  Purchase #7 $180.69   11.719%   $201.8651   $201.87   $201.85   $201.90  
  7 purchase totals = $986.72       $1,085.3007   $1,085.31   $1,085.25   $1,085.30