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 $61.97   7.182%   $66.4207   $66.42   $66.40   $66.40  
  Purchase #2 $223.70   6.689%   $238.6633   $238.66   $238.65   $238.70  
  Purchase #3 $194.95   7.458%   $209.4894   $209.49   $209.50   $209.50  
  Purchase #4 $88.77   3.322%   $91.7189   $91.72   $91.70   $91.70  
  Purchase #5 $11.46   8.151%   $12.3941   $12.39   $12.40   $12.40  
  Purchase #6 $194.47   12.852%   $219.4633   $219.46   $219.45   $219.50  
  Purchase #7 $105.49   3.552%   $109.237   $109.24   $109.25   $109.20  
  7 purchase totals = $880.81       $947.3867   $947.38   $947.35   $947.40