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 $5.55   10.440%   $6.1294   $6.13   $6.15   $6.10  
  Purchase #2 $70.83   13.539%   $80.4197   $80.42   $80.40   $80.40  
  Purchase #3 $59.29   8.315%   $64.22   $64.22   $64.20   $64.20  
  Purchase #4 $194.82   6.535%   $207.5515   $207.55   $207.55   $207.60  
  Purchase #5 $155.86   10.320%   $171.9448   $171.94   $171.95   $171.90  
  Purchase #6 $21.59   12.306%   $24.2469   $24.25   $24.25   $24.20  
  Purchase #7 $144.75   13.542%   $164.352   $164.35   $164.35   $164.40  
  7 purchase totals = $652.69       $718.8643   $718.86   $718.85   $718.80