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 $92.44   6.286%   $98.2508   $98.25   $98.25   $98.30  
  Purchase #2 $202.93   13.131%   $229.5767   $229.58   $229.60   $229.60  
  Purchase #3 $147.90   13.228%   $167.4642   $167.46   $167.45   $167.50  
  Purchase #4 $157.81   5.232%   $166.0666   $166.07   $166.05   $166.10  
  Purchase #5 $165.33   8.159%   $178.8193   $178.82   $178.80   $178.80  
  Purchase #6 $200.80   8.588%   $218.0447   $218.04   $218.05   $218.00  
  Purchase #7 $207.61   8.495%   $225.2465   $225.25   $225.25   $225.20  
  7 purchase totals = $1,174.82       $1,283.4688   $1,283.47   $1,283.45   $1,283.50