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 $113.32   11.822%   $126.7167   $126.72   $126.70   $126.70  
  Purchase #2 $201.92   8.870%   $219.8303   $219.83   $219.85   $219.80  
  Purchase #3 $171.67   7.489%   $184.5264   $184.53   $184.55   $184.50  
  Purchase #4 $176.92   5.364%   $186.41   $186.41   $186.40   $186.40  
  Purchase #5 $63.54   10.767%   $70.3814   $70.38   $70.40   $70.40  
  Purchase #6 $235.43   4.860%   $246.8719   $246.87   $246.85   $246.90  
  Purchase #7 $132.50   5.788%   $140.1691   $140.17   $140.15   $140.20  
  7 purchase totals = $1,095.30       $1,174.9058   $1,174.91   $1,174.90   $1,174.90