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 $101.29   13.307%   $114.7687   $114.77   $114.75   $114.80  
  Purchase #2 $194.80   4.191%   $202.9641   $202.96   $202.95   $203.00  
  Purchase #3 $50.46   4.806%   $52.8851   $52.89   $52.90   $52.90  
  Purchase #4 $77.77   4.382%   $81.1779   $81.18   $81.20   $81.20  
  Purchase #5 $127.26   3.610%   $131.8541   $131.85   $131.85   $131.90  
  Purchase #6 $205.89   6.128%   $218.5069   $218.51   $218.50   $218.50  
  Purchase #7 $197.78   6.303%   $210.2461   $210.25   $210.25   $210.20  
  7 purchase totals = $955.25       $1,012.4029   $1,012.41   $1,012.40   $1,012.50