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 $194.38   10.282%   $214.3662   $214.37   $214.35   $214.40  
  Purchase #2 $203.99   11.656%   $227.7671   $227.77   $227.75   $227.80  
  Purchase #3 $42.81   8.385%   $46.3996   $46.40   $46.40   $46.40  
  Purchase #4 $232.38   11.216%   $258.4437   $258.44   $258.45   $258.40  
  Purchase #5 $17.82   6.146%   $18.9152   $18.92   $18.90   $18.90  
  Purchase #6 $115.41   8.754%   $125.513   $125.51   $125.50   $125.50  
  Purchase #7 $167.82   7.580%   $180.5408   $180.54   $180.55   $180.50  
  7 purchase totals = $974.61       $1,071.9456   $1,071.95   $1,071.90   $1,071.90