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 $61.83   3.219%   $63.8203   $63.82   $63.80   $63.80  
  Purchase #2 $167.98   5.172%   $176.6679   $176.67   $176.65   $176.70  
  Purchase #3 $228.35   9.462%   $249.9565   $249.96   $249.95   $250.00  
  Purchase #4 $36.87   13.410%   $41.8143   $41.81   $41.80   $41.80  
  Purchase #5 $118.33   7.337%   $127.0119   $127.01   $127.00   $127.00  
  Purchase #6 $172.99   6.699%   $184.5786   $184.58   $184.60   $184.60  
  Purchase #7 $96.69   12.576%   $108.8497   $108.85   $108.85   $108.80  
  7 purchase totals = $883.04       $952.6992   $952.70   $952.65   $952.70