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 $246.29   12.573%   $277.256   $277.26   $277.25   $277.30  
  Purchase #2 $101.30   12.584%   $114.0476   $114.05   $114.05   $114.00  
  Purchase #3 $92.28   6.318%   $98.1103   $98.11   $98.10   $98.10  
  Purchase #4 $224.49   13.155%   $254.0217   $254.02   $254.00   $254.00  
  Purchase #5 $246.49   9.445%   $269.771   $269.77   $269.75   $269.80  
  Purchase #6 $165.75   9.438%   $181.3935   $181.39   $181.40   $181.40  
  Purchase #7 $37.90   10.664%   $41.9417   $41.94   $41.95   $41.90  
  7 purchase totals = $1,114.50       $1,236.5418   $1,236.54   $1,236.50   $1,236.50