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 $208.79   8.198%   $225.9066   $225.91   $225.90   $225.90  
  Purchase #2 $52.34   7.259%   $56.1394   $56.14   $56.15   $56.10  
  Purchase #3 $243.72   9.110%   $265.9229   $265.92   $265.90   $265.90  
  Purchase #4 $71.47   6.435%   $76.0691   $76.07   $76.05   $76.10  
  Purchase #5 $46.41   3.647%   $48.1026   $48.10   $48.10   $48.10  
  Purchase #6 $247.37   8.341%   $268.0031   $268.00   $268.00   $268.00  
  Purchase #7 $136.57   12.284%   $153.3463   $153.35   $153.35   $153.30  
  7 purchase totals = $1,006.67       $1,093.4900   $1,093.49   $1,093.45   $1,093.40