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 $66.53   10.466%   $73.493   $73.49   $73.50   $73.50  
  Purchase #2 $215.30   6.231%   $228.7153   $228.72   $228.70   $228.70  
  Purchase #3 $153.85   13.541%   $174.6828   $174.68   $174.70   $174.70  
  Purchase #4 $169.78   9.864%   $186.5271   $186.53   $186.55   $186.50  
  Purchase #5 $182.95   13.529%   $207.7013   $207.70   $207.70   $207.70  
  Purchase #6 $23.66   5.634%   $24.993   $24.99   $25.00   $25.00  
  Purchase #7 $29.68   9.175%   $32.4031   $32.40   $32.40   $32.40  
  7 purchase totals = $841.75       $928.5156   $928.51   $928.55   $928.50