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 $250.90   6.668%   $267.63   $267.63   $267.65   $267.60  
  Purchase #2 $91.36   9.309%   $99.8647   $99.86   $99.85   $99.90  
  Purchase #3 $84.75   3.410%   $87.64   $87.64   $87.65   $87.60  
  Purchase #4 $192.79   7.753%   $207.737   $207.74   $207.75   $207.70  
  Purchase #5 $10.81   10.462%   $11.9409   $11.94   $11.95   $11.90  
  Purchase #6 $29.99   4.376%   $31.3024   $31.30   $31.30   $31.30  
  Purchase #7 $43.51   13.701%   $49.4713   $49.47   $49.45   $49.50  
  7 purchase totals = $704.11       $755.5863   $755.58   $755.60   $755.50