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 $60.51   9.658%   $66.3541   $66.35   $66.35   $66.40  
  Purchase #2 $188.87   6.747%   $201.6131   $201.61   $201.60   $201.60  
  Purchase #3 $189.57   8.425%   $205.5413   $205.54   $205.55   $205.50  
  Purchase #4 $29.83   3.693%   $30.9316   $30.93   $30.95   $30.90  
  Purchase #5 $10.38   4.437%   $10.8406   $10.84   $10.85   $10.80  
  Purchase #6 $103.80   4.524%   $108.4959   $108.50   $108.50   $108.50  
  Purchase #7 $119.63   3.628%   $123.9702   $123.97   $123.95   $124.00  
  7 purchase totals = $702.59       $747.7468   $747.74   $747.75   $747.70