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 $60.63   13.736%   $68.9581   $68.96   $68.95   $69.00  
  Purchase #2 $180.54   13.272%   $204.5013   $204.50   $204.50   $204.50  
  Purchase #3 $86.25   10.626%   $95.4149   $95.41   $95.40   $95.40  
  Purchase #4 $169.49   7.761%   $182.6441   $182.64   $182.65   $182.60  
  Purchase #5 $243.96   5.750%   $257.9877   $257.99   $258.00   $258.00  
  Purchase #6 $189.90   10.439%   $209.7237   $209.72   $209.70   $209.70  
  Purchase #7 $112.87   7.516%   $121.3533   $121.35   $121.35   $121.40  
  7 purchase totals = $1,043.64       $1,140.5831   $1,140.57   $1,140.55   $1,140.60