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 $64.58   3.493%   $66.8358   $66.84   $66.85   $66.80  
  Purchase #2 $71.94   5.155%   $75.6485   $75.65   $75.65   $75.60  
  Purchase #3 $155.29   5.670%   $164.0949   $164.09   $164.10   $164.10  
  Purchase #4 $66.54   7.658%   $71.6356   $71.64   $71.65   $71.60  
  Purchase #5 $88.50   5.581%   $93.4392   $93.44   $93.45   $93.40  
  Purchase #6 $5.85   12.703%   $6.5931   $6.59   $6.60   $6.60  
  Purchase #7 $226.81   11.558%   $253.0247   $253.02   $253.00   $253.00  
  7 purchase totals = $679.51       $731.2718   $731.27   $731.30   $731.10