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 $241.29   10.771%   $267.2793   $267.28   $267.30   $267.30  
  Purchase #2 $161.34   13.333%   $182.8515   $182.85   $182.85   $182.90  
  Purchase #3 $114.37   4.375%   $119.3737   $119.37   $119.35   $119.40  
  Purchase #4 $223.46   10.207%   $246.2686   $246.27   $246.25   $246.30  
  Purchase #5 $37.28   3.595%   $38.6202   $38.62   $38.60   $38.60  
  Purchase #6 $102.40   9.840%   $112.4762   $112.48   $112.50   $112.50  
  Purchase #7 $204.68   10.445%   $226.0588   $226.06   $226.05   $226.10  
  7 purchase totals = $1,084.82       $1,192.9283   $1,192.93   $1,192.90   $1,193.10