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 $60.48   4.651%   $63.2929   $63.29   $63.30   $63.30  
  Purchase #2 $215.77   12.723%   $243.2224   $243.22   $243.20   $243.20  
  Purchase #3 $184.49   5.230%   $194.1388   $194.14   $194.15   $194.10  
  Purchase #4 $83.85   11.669%   $93.6345   $93.63   $93.65   $93.60  
  Purchase #5 $98.69   4.844%   $103.4705   $103.47   $103.45   $103.50  
  Purchase #6 $24.94   5.868%   $26.4035   $26.40   $26.40   $26.40  
  Purchase #7 $72.68   9.183%   $79.3542   $79.35   $79.35   $79.40  
  7 purchase totals = $740.90       $803.5168   $803.50   $803.50   $803.50