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 $174.38   9.671%   $191.2443   $191.24   $191.25   $191.20  
  Purchase #2 $125.27   5.602%   $132.2876   $132.29   $132.30   $132.30  
  Purchase #3 $116.32   11.565%   $129.7724   $129.77   $129.75   $129.80  
  Purchase #4 $102.88   4.159%   $107.1588   $107.16   $107.15   $107.20  
  Purchase #5 $200.98   11.409%   $223.9098   $223.91   $223.90   $223.90  
  Purchase #6 $136.51   12.248%   $153.2297   $153.23   $153.25   $153.20  
  Purchase #7 $238.79   11.394%   $265.9977   $266.00   $266.00   $266.00  
  7 purchase totals = $1,095.13       $1,203.6003   $1,203.60   $1,203.60   $1,203.60