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 $179.86   13.201%   $203.6033   $203.60   $203.60   $203.60  
  Purchase #2 $104.51   8.190%   $113.0694   $113.07   $113.05   $113.10  
  Purchase #3 $26.66   12.224%   $29.9189   $29.92   $29.90   $29.90  
  Purchase #4 $93.59   4.242%   $97.5601   $97.56   $97.55   $97.60  
  Purchase #5 $180.92   7.347%   $194.2122   $194.21   $194.20   $194.20  
  Purchase #6 $182.27   6.419%   $193.9699   $193.97   $193.95   $194.00  
  Purchase #7 $196.61   11.524%   $219.2673   $219.27   $219.25   $219.30  
  7 purchase totals = $964.42       $1,051.6011   $1,051.60   $1,051.50   $1,051.70