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 $243.48   13.737%   $276.9268   $276.93   $276.95   $276.90  
  Purchase #2 $169.29   7.277%   $181.6092   $181.61   $181.60   $181.60  
  Purchase #3 $198.92   8.149%   $215.13   $215.13   $215.15   $215.10  
  Purchase #4 $12.57   7.348%   $13.4936   $13.49   $13.50   $13.50  
  Purchase #5 $246.55   9.218%   $269.277   $269.28   $269.30   $269.30  
  Purchase #6 $130.43   4.247%   $135.9694   $135.97   $135.95   $136.00  
  Purchase #7 $166.78   4.560%   $174.3852   $174.39   $174.40   $174.40  
  7 purchase totals = $1,168.02       $1,266.7912   $1,266.80   $1,266.85   $1,266.80