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 $189.57   8.544%   $205.7669   $205.77   $205.75   $205.80  
  Purchase #2 $55.90   6.609%   $59.5944   $59.59   $59.60   $59.60  
  Purchase #3 $101.86   5.723%   $107.6894   $107.69   $107.70   $107.70  
  Purchase #4 $174.91   8.376%   $189.5605   $189.56   $189.55   $189.60  
  Purchase #5 $82.77   13.781%   $94.1765   $94.18   $94.20   $94.20  
  Purchase #6 $134.68   9.851%   $147.9473   $147.95   $147.95   $147.90  
  Purchase #7 $199.86   13.432%   $226.7052   $226.71   $226.70   $226.70  
  7 purchase totals = $939.55       $1,031.4402   $1,031.45   $1,031.45   $1,031.50