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 $116.81   11.824%   $130.6216   $130.62   $130.60   $130.60  
  Purchase #2 $61.83   8.261%   $66.9378   $66.94   $66.95   $66.90  
  Purchase #3 $241.96   12.732%   $272.7663   $272.77   $272.75   $272.80  
  Purchase #4 $68.75   11.421%   $76.6019   $76.60   $76.60   $76.60  
  Purchase #5 $184.97   8.181%   $200.1024   $200.10   $200.10   $200.10  
  Purchase #6 $113.30   8.342%   $122.7515   $122.75   $122.75   $122.80  
  Purchase #7 $147.65   9.354%   $161.4612   $161.46   $161.45   $161.50  
  7 purchase totals = $935.27       $1,031.2427   $1,031.24   $1,031.20   $1,031.30