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 $63.63   12.262%   $71.4323   $71.43   $71.45   $71.40  
  Purchase #2 $189.43   6.557%   $201.8509   $201.85   $201.85   $201.90  
  Purchase #3 $52.34   13.495%   $59.4033   $59.40   $59.40   $59.40  
  Purchase #4 $190.72   6.217%   $202.5771   $202.58   $202.60   $202.60  
  Purchase #5 $62.92   5.639%   $66.4681   $66.47   $66.45   $66.50  
  Purchase #6 $21.60   10.630%   $23.8961   $23.90   $23.90   $23.90  
  Purchase #7 $101.73   6.707%   $108.553   $108.55   $108.55   $108.60  
  7 purchase totals = $682.37       $734.1808   $734.18   $734.20   $734.30