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 $219.62   12.299%   $246.6311   $246.63   $246.65   $246.60  
  Purchase #2 $241.71   10.249%   $266.4829   $266.48   $266.50   $266.50  
  Purchase #3 $40.83   12.237%   $45.8264   $45.83   $45.85   $45.80  
  Purchase #4 $97.34   7.333%   $104.4779   $104.48   $104.50   $104.50  
  Purchase #5 $163.59   6.515%   $174.2479   $174.25   $174.25   $174.20  
  Purchase #6 $33.31   3.162%   $34.3633   $34.36   $34.35   $34.40  
  Purchase #7 $128.47   6.115%   $136.3259   $136.33   $136.35   $136.30  
  7 purchase totals = $924.87       $1,008.3554   $1,008.36   $1,008.45   $1,008.30