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 $116.26   13.492%   $131.9458   $131.95   $131.95   $131.90  
  Purchase #2 $235.58   8.205%   $254.9093   $254.91   $254.90   $254.90  
  Purchase #3 $102.67   3.557%   $106.322   $106.32   $106.30   $106.30  
  Purchase #4 $234.72   7.377%   $252.0353   $252.04   $252.05   $252.00  
  Purchase #5 $109.95   8.476%   $119.2694   $119.27   $119.25   $119.30  
  Purchase #6 $189.96   3.639%   $196.8726   $196.87   $196.85   $196.90  
  Purchase #7 $168.53   6.757%   $179.9176   $179.92   $179.90   $179.90  
  7 purchase totals = $1,157.67       $1,241.2720   $1,241.28   $1,241.20   $1,241.20