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 $250.74   9.780%   $275.2624   $275.26   $275.25   $275.30  
  Purchase #2 $206.76   4.416%   $215.8905   $215.89   $215.90   $215.90  
  Purchase #3 $26.26   5.816%   $27.7873   $27.79   $27.80   $27.80  
  Purchase #4 $111.53   7.324%   $119.6985   $119.70   $119.70   $119.70  
  Purchase #5 $81.70   8.140%   $88.3504   $88.35   $88.35   $88.40  
  Purchase #6 $204.86   4.183%   $213.4293   $213.43   $213.45   $213.40  
  Purchase #7 $80.80   13.529%   $91.7314   $91.73   $91.75   $91.70  
  7 purchase totals = $962.65       $1,032.1498   $1,032.15   $1,032.20   $1,032.20