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 $85.77   12.648%   $96.6182   $96.62   $96.60   $96.60  
  Purchase #2 $190.81   10.861%   $211.5339   $211.53   $211.55   $211.50  
  Purchase #3 $124.70   8.753%   $135.615   $135.62   $135.60   $135.60  
  Purchase #4 $232.40   11.669%   $259.5188   $259.52   $259.50   $259.50  
  Purchase #5 $214.33   7.747%   $230.9341   $230.93   $230.95   $230.90  
  Purchase #6 $50.67   6.263%   $53.8435   $53.84   $53.85   $53.80  
  Purchase #7 $117.84   10.789%   $130.5538   $130.55   $130.55   $130.60  
  7 purchase totals = $1,016.52       $1,118.6173   $1,118.61   $1,118.60   $1,118.50