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 $65.41   12.559%   $73.6248   $73.62   $73.60   $73.60  
  Purchase #2 $98.97   5.560%   $104.4727   $104.47   $104.45   $104.50  
  Purchase #3 $219.87   9.547%   $240.861   $240.86   $240.85   $240.90  
  Purchase #4 $93.83   13.415%   $106.4173   $106.42   $106.40   $106.40  
  Purchase #5 $6.35   6.786%   $6.7809   $6.78   $6.80   $6.80  
  Purchase #6 $96.79   7.357%   $103.9108   $103.91   $103.90   $103.90  
  Purchase #7 $90.40   8.819%   $98.3724   $98.37   $98.35   $98.40  
  7 purchase totals = $671.62       $734.4399   $734.43   $734.35   $734.50