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 $22.66   10.135%   $24.9566   $24.96   $24.95   $25.00  
  Purchase #2 $102.58   8.451%   $111.249   $111.25   $111.25   $111.20  
  Purchase #3 $219.43   10.172%   $241.7504   $241.75   $241.75   $241.80  
  Purchase #4 $56.77   3.778%   $58.9148   $58.91   $58.90   $58.90  
  Purchase #5 $240.25   12.766%   $270.9203   $270.92   $270.90   $270.90  
  Purchase #6 $167.75   6.416%   $178.5128   $178.51   $178.50   $178.50  
  Purchase #7 $131.74   7.321%   $141.3847   $141.38   $141.40   $141.40  
  7 purchase totals = $941.18       $1,027.6886   $1,027.68   $1,027.65   $1,027.70