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 $236.89   13.783%   $269.5405   $269.54   $269.55   $269.50  
  Purchase #2 $33.49   7.470%   $35.9917   $35.99   $36.00   $36.00  
  Purchase #3 $212.44   3.465%   $219.801   $219.80   $219.80   $219.80  
  Purchase #4 $241.55   13.444%   $274.024   $274.02   $274.00   $274.00  
  Purchase #5 $161.69   4.607%   $169.1391   $169.14   $169.15   $169.10  
  Purchase #6 $112.89   4.792%   $118.2997   $118.30   $118.30   $118.30  
  Purchase #7 $198.49   6.442%   $211.2767   $211.28   $211.30   $211.30  
  7 purchase totals = $1,197.44       $1,298.0727   $1,298.07   $1,298.10   $1,298.00