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 $227.92   11.723%   $254.6391   $254.64   $254.65   $254.60  
  Purchase #2 $165.47   9.490%   $181.1731   $181.17   $181.15   $181.20  
  Purchase #3 $146.63   11.106%   $162.9147   $162.91   $162.90   $162.90  
  Purchase #4 $142.27   6.198%   $151.0879   $151.09   $151.10   $151.10  
  Purchase #5 $104.74   11.768%   $117.0658   $117.07   $117.05   $117.10  
  Purchase #6 $148.61   8.572%   $161.3488   $161.35   $161.35   $161.30  
  Purchase #7 $56.79   3.364%   $58.7004   $58.70   $58.70   $58.70  
  7 purchase totals = $992.43       $1,086.9298   $1,086.93   $1,086.90   $1,086.90