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 $80.66   5.823%   $85.3568   $85.36   $85.35   $85.40  
  Purchase #2 $233.25   9.405%   $255.1872   $255.19   $255.20   $255.20  
  Purchase #3 $227.29   8.616%   $246.8733   $246.87   $246.85   $246.90  
  Purchase #4 $222.58   11.366%   $247.8784   $247.88   $247.90   $247.90  
  Purchase #5 $86.30   6.215%   $91.6635   $91.66   $91.65   $91.70  
  Purchase #6 $84.30   10.735%   $93.3496   $93.35   $93.35   $93.30  
  Purchase #7 $205.26   7.860%   $221.3934   $221.39   $221.40   $221.40  
  7 purchase totals = $1,139.64       $1,241.7022   $1,241.70   $1,241.70   $1,241.80