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 $31.52   12.331%   $35.4067   $35.41   $35.40   $35.40  
  Purchase #2 $175.88   4.413%   $183.6416   $183.64   $183.65   $183.60  
  Purchase #3 $78.71   5.563%   $83.0886   $83.09   $83.10   $83.10  
  Purchase #4 $177.77   12.605%   $200.1779   $200.18   $200.20   $200.20  
  Purchase #5 $208.28   7.803%   $224.5321   $224.53   $224.55   $224.50  
  Purchase #6 $150.26   10.757%   $166.4235   $166.42   $166.40   $166.40  
  Purchase #7 $134.91   4.817%   $141.4086   $141.41   $141.40   $141.40  
  7 purchase totals = $957.33       $1,034.6790   $1,034.68   $1,034.70   $1,034.60