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 $247.87   6.365%   $263.6469   $263.65   $263.65   $263.60  
  Purchase #2 $156.63   11.505%   $174.6503   $174.65   $174.65   $174.70  
  Purchase #3 $194.87   11.715%   $217.699   $217.70   $217.70   $217.70  
  Purchase #4 $67.86   6.639%   $72.3652   $72.37   $72.35   $72.40  
  Purchase #5 $57.25   6.431%   $60.9317   $60.93   $60.95   $60.90  
  Purchase #6 $91.64   11.567%   $102.24   $102.24   $102.25   $102.20  
  Purchase #7 $198.32   4.362%   $206.9707   $206.97   $206.95   $207.00  
  7 purchase totals = $1,014.44       $1,098.5038   $1,098.51   $1,098.50   $1,098.50