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 $53.82   13.711%   $61.1993   $61.20   $61.20   $61.20  
  Purchase #2 $219.87   10.502%   $242.9607   $242.96   $242.95   $243.00  
  Purchase #3 $128.83   9.493%   $141.0598   $141.06   $141.05   $141.10  
  Purchase #4 $199.67   4.313%   $208.2818   $208.28   $208.30   $208.30  
  Purchase #5 $15.89   10.378%   $17.5391   $17.54   $17.55   $17.50  
  Purchase #6 $155.85   4.840%   $163.3931   $163.39   $163.40   $163.40  
  Purchase #7 $10.52   5.213%   $11.0684   $11.07   $11.05   $11.10  
  7 purchase totals = $784.45       $845.5022   $845.50   $845.50   $845.60