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 $183.63   6.174%   $194.9673   $194.97   $194.95   $195.00  
  Purchase #2 $209.73   4.421%   $219.0022   $219.00   $219.00   $219.00  
  Purchase #3 $62.98   13.233%   $71.3141   $71.31   $71.30   $71.30  
  Purchase #4 $148.77   8.714%   $161.7338   $161.73   $161.75   $161.70  
  Purchase #5 $30.94   13.324%   $35.0624   $35.06   $35.05   $35.10  
  Purchase #6 $211.32   7.316%   $226.7802   $226.78   $226.80   $226.80  
  Purchase #7 $173.90   5.216%   $182.9706   $182.97   $182.95   $183.00  
  7 purchase totals = $1,021.27       $1,091.8306   $1,091.82   $1,091.80   $1,091.90