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 $66.34   6.392%   $70.5805   $70.58   $70.60   $70.60  
  Purchase #2 $47.94   10.196%   $52.828   $52.83   $52.85   $52.80  
  Purchase #3 $183.76   5.841%   $194.4934   $194.49   $194.50   $194.50  
  Purchase #4 $221.51   7.203%   $237.4654   $237.47   $237.45   $237.50  
  Purchase #5 $96.60   4.505%   $100.9518   $100.95   $100.95   $101.00  
  Purchase #6 $187.25   13.239%   $212.04   $212.04   $212.05   $212.00  
  Purchase #7 $232.54   10.778%   $257.6032   $257.60   $257.60   $257.60  
  7 purchase totals = $1,035.94       $1,125.9623   $1,125.96   $1,126.00   $1,126.00