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 $58.62   11.291%   $65.2388   $65.24   $65.25   $65.20  
  Purchase #2 $241.81   5.142%   $254.2439   $254.24   $254.25   $254.20  
  Purchase #3 $96.46   6.353%   $102.5881   $102.59   $102.60   $102.60  
  Purchase #4 $161.98   13.475%   $183.8068   $183.81   $183.80   $183.80  
  Purchase #5 $248.90   8.674%   $270.4896   $270.49   $270.50   $270.50  
  Purchase #6 $122.31   3.181%   $126.2007   $126.20   $126.20   $126.20  
  Purchase #7 $32.56   10.124%   $35.8564   $35.86   $35.85   $35.90  
  7 purchase totals = $962.64       $1,038.4243   $1,038.43   $1,038.45   $1,038.40