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 $61.46   8.424%   $66.6374   $66.64   $66.65   $66.60  
  Purchase #2 $68.68   4.842%   $72.0055   $72.01   $72.00   $72.00  
  Purchase #3 $99.81   5.721%   $105.5201   $105.52   $105.50   $105.50  
  Purchase #4 $191.91   4.286%   $200.1353   $200.14   $200.15   $200.10  
  Purchase #5 $206.81   13.434%   $234.5929   $234.59   $234.60   $234.60  
  Purchase #6 $114.44   9.459%   $125.2649   $125.26   $125.25   $125.30  
  Purchase #7 $6.51   9.221%   $7.1103   $7.11   $7.10   $7.10  
  7 purchase totals = $749.62       $811.2664   $811.27   $811.25   $811.20