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 $246.75   10.173%   $271.8519   $271.85   $271.85   $271.90  
  Purchase #2 $173.81   13.736%   $197.6845   $197.68   $197.70   $197.70  
  Purchase #3 $138.81   12.592%   $156.289   $156.29   $156.30   $156.30  
  Purchase #4 $244.59   4.177%   $254.8065   $254.81   $254.80   $254.80  
  Purchase #5 $43.54   11.454%   $48.5271   $48.53   $48.55   $48.50  
  Purchase #6 $126.37   4.432%   $131.9707   $131.97   $131.95   $132.00  
  Purchase #7 $29.47   10.494%   $32.5626   $32.56   $32.55   $32.60  
  7 purchase totals = $1,003.34       $1,093.6923   $1,093.69   $1,093.70   $1,093.80