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 $91.28   3.667%   $94.6272   $94.63   $94.65   $94.60  
  Purchase #2 $241.43   9.412%   $264.1534   $264.15   $264.15   $264.20  
  Purchase #3 $206.42   11.752%   $230.6785   $230.68   $230.70   $230.70  
  Purchase #4 $206.32   9.701%   $226.3351   $226.34   $226.35   $226.30  
  Purchase #5 $106.79   9.652%   $117.0974   $117.10   $117.10   $117.10  
  Purchase #6 $201.51   6.449%   $214.5054   $214.51   $214.50   $214.50  
  Purchase #7 $158.81   13.133%   $179.6665   $179.67   $179.65   $179.70  
  7 purchase totals = $1,212.56       $1,327.0635   $1,327.08   $1,327.10   $1,327.10