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 $99.30   4.361%   $103.6305   $103.63   $103.65   $103.60  
  Purchase #2 $98.33   4.541%   $102.7952   $102.80   $102.80   $102.80  
  Purchase #3 $245.54   3.816%   $254.9098   $254.91   $254.90   $254.90  
  Purchase #4 $119.42   3.396%   $123.4755   $123.48   $123.50   $123.50  
  Purchase #5 $197.70   13.457%   $224.3045   $224.30   $224.30   $224.30  
  Purchase #6 $114.90   12.286%   $129.0166   $129.02   $129.00   $129.00  
  Purchase #7 $56.71   7.110%   $60.7421   $60.74   $60.75   $60.70  
  7 purchase totals = $931.90       $998.8742   $998.88   $998.90   $998.80