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 $31.96   6.706%   $34.1032   $34.10   $34.10   $34.10  
  Purchase #2 $60.54   10.635%   $66.9784   $66.98   $67.00   $67.00  
  Purchase #3 $218.46   5.318%   $230.0777   $230.08   $230.10   $230.10  
  Purchase #4 $62.69   8.602%   $68.0826   $68.08   $68.10   $68.10  
  Purchase #5 $226.85   4.538%   $237.1445   $237.14   $237.15   $237.10  
  Purchase #6 $8.56   4.557%   $8.9501   $8.95   $8.95   $9.00  
  Purchase #7 $58.88   10.739%   $65.2031   $65.20   $65.20   $65.20  
  7 purchase totals = $667.94       $710.5396   $710.53   $710.60   $710.60