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 $87.64   12.215%   $98.3452   $98.35   $98.35   $98.30  
  Purchase #2 $167.87   9.617%   $184.0141   $184.01   $184.00   $184.00  
  Purchase #3 $207.37   7.495%   $222.9124   $222.91   $222.90   $222.90  
  Purchase #4 $169.47   4.808%   $177.6181   $177.62   $177.60   $177.60  
  Purchase #5 $86.57   11.544%   $96.5636   $96.56   $96.55   $96.60  
  Purchase #6 $102.86   12.416%   $115.6311   $115.63   $115.65   $115.60  
  Purchase #7 $141.34   8.848%   $153.8458   $153.85   $153.85   $153.80  
  7 purchase totals = $963.12       $1,048.9303   $1,048.93   $1,048.90   $1,048.80