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 $233.98   6.525%   $249.2472   $249.25   $249.25   $249.20  
  Purchase #2 $201.41   8.710%   $218.9528   $218.95   $218.95   $219.00  
  Purchase #3 $115.28   7.432%   $123.8476   $123.85   $123.85   $123.80  
  Purchase #4 $197.72   11.715%   $220.8829   $220.88   $220.90   $220.90  
  Purchase #5 $164.31   9.717%   $180.276   $180.28   $180.30   $180.30  
  Purchase #6 $236.48   10.849%   $262.1357   $262.14   $262.15   $262.10  
  Purchase #7 $37.80   4.784%   $39.6084   $39.61   $39.60   $39.60  
  7 purchase totals = $1,186.98       $1,294.9506   $1,294.96   $1,295.00   $1,294.90