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 $60.35   3.731%   $62.6017   $62.60   $62.60   $62.60  
  Purchase #2 $58.25   5.143%   $61.2458   $61.25   $61.25   $61.20  
  Purchase #3 $58.26   5.259%   $61.3239   $61.32   $61.30   $61.30  
  Purchase #4 $163.51   8.266%   $177.0257   $177.03   $177.05   $177.00  
  Purchase #5 $153.57   8.311%   $166.3332   $166.33   $166.35   $166.30  
  Purchase #6 $8.57   11.281%   $9.5368   $9.54   $9.55   $9.50  
  Purchase #7 $181.85   4.813%   $190.6024   $190.60   $190.60   $190.60  
  7 purchase totals = $684.36       $728.6695   $728.67   $728.70   $728.50