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 $231.81   6.824%   $247.6287   $247.63   $247.65   $247.60  
  Purchase #2 $76.42   13.292%   $86.5777   $86.58   $86.60   $86.60  
  Purchase #3 $204.59   13.620%   $232.4552   $232.46   $232.45   $232.50  
  Purchase #4 $124.39   11.258%   $138.3938   $138.39   $138.40   $138.40  
  Purchase #5 $161.55   3.410%   $167.0589   $167.06   $167.05   $167.10  
  Purchase #6 $208.47   5.600%   $220.1443   $220.14   $220.15   $220.10  
  Purchase #7 $64.29   4.362%   $67.0943   $67.09   $67.10   $67.10  
  7 purchase totals = $1,071.52       $1,159.3529   $1,159.35   $1,159.40   $1,159.40