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 $40.97   6.609%   $43.6777   $43.68   $43.70   $43.70  
  Purchase #2 $211.96   8.492%   $229.9596   $229.96   $229.95   $230.00  
  Purchase #3 $46.71   10.480%   $51.6052   $51.61   $51.60   $51.60  
  Purchase #4 $119.97   6.615%   $127.906   $127.91   $127.90   $127.90  
  Purchase #5 $109.88   6.452%   $116.9695   $116.97   $116.95   $117.00  
  Purchase #6 $113.46   9.783%   $124.5598   $124.56   $124.55   $124.60  
  Purchase #7 $94.79   7.585%   $101.9798   $101.98   $102.00   $102.00  
  7 purchase totals = $737.74       $796.6576   $796.67   $796.65   $796.80