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 $27.36   8.287%   $29.6273   $29.63   $29.65   $29.60  
  Purchase #2 $169.59   8.607%   $184.1866   $184.19   $184.20   $184.20  
  Purchase #3 $107.40   10.254%   $118.4128   $118.41   $118.40   $118.40  
  Purchase #4 $234.77   8.864%   $255.58   $255.58   $255.60   $255.60  
  Purchase #5 $247.82   12.297%   $278.2944   $278.29   $278.30   $278.30  
  Purchase #6 $13.51   9.630%   $14.811   $14.81   $14.80   $14.80  
  Purchase #7 $224.33   9.799%   $246.3121   $246.31   $246.30   $246.30  
  7 purchase totals = $1,024.78       $1,127.2242   $1,127.22   $1,127.25   $1,127.20