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 $202.45   12.488%   $227.732   $227.73   $227.75   $227.70  
  Purchase #2 $78.59   8.105%   $84.9597   $84.96   $84.95   $85.00  
  Purchase #3 $158.92   5.110%   $167.0408   $167.04   $167.05   $167.00  
  Purchase #4 $166.42   12.657%   $187.4838   $187.48   $187.50   $187.50  
  Purchase #5 $31.69   13.276%   $35.8972   $35.90   $35.90   $35.90  
  Purchase #6 $250.41   13.124%   $283.2738   $283.27   $283.25   $283.30  
  Purchase #7 $34.55   12.819%   $38.979   $38.98   $39.00   $39.00  
  7 purchase totals = $923.03       $1,025.3663   $1,025.36   $1,025.40   $1,025.40