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 $226.62   9.517%   $248.1874   $248.19   $248.20   $248.20  
  Purchase #2 $62.71   5.326%   $66.0499   $66.05   $66.05   $66.00  
  Purchase #3 $161.33   6.424%   $171.6938   $171.69   $171.70   $171.70  
  Purchase #4 $10.94   6.635%   $11.6659   $11.67   $11.65   $11.70  
  Purchase #5 $216.73   12.205%   $243.1819   $243.18   $243.20   $243.20  
  Purchase #6 $240.88   5.842%   $254.9522   $254.95   $254.95   $255.00  
  Purchase #7 $168.47   9.856%   $185.0744   $185.07   $185.05   $185.10  
  7 purchase totals = $1,087.68       $1,180.8055   $1,180.80   $1,180.80   $1,180.90