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 $87.49   7.821%   $94.3326   $94.33   $94.35   $94.30  
  Purchase #2 $242.33   10.469%   $267.6995   $267.70   $267.70   $267.70  
  Purchase #3 $129.37   4.277%   $134.9032   $134.90   $134.90   $134.90  
  Purchase #4 $6.53   7.659%   $7.0301   $7.03   $7.05   $7.00  
  Purchase #5 $245.35   5.829%   $259.6515   $259.65   $259.65   $259.70  
  Purchase #6 $187.98   9.580%   $205.9885   $205.99   $206.00   $206.00  
  Purchase #7 $184.57   13.114%   $208.7745   $208.77   $208.75   $208.80  
  7 purchase totals = $1,083.62       $1,178.3799   $1,178.37   $1,178.40   $1,178.40