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 $54.83   7.563%   $58.9768   $58.98   $59.00   $59.00  
  Purchase #2 $250.97   10.610%   $277.5979   $277.60   $277.60   $277.60  
  Purchase #3 $194.48   3.245%   $200.7909   $200.79   $200.80   $200.80  
  Purchase #4 $220.32   6.164%   $233.9005   $233.90   $233.90   $233.90  
  Purchase #5 $173.51   8.238%   $187.8038   $187.80   $187.80   $187.80  
  Purchase #6 $127.48   12.366%   $143.2442   $143.24   $143.25   $143.20  
  Purchase #7 $67.40   9.623%   $73.8859   $73.89   $73.90   $73.90  
  7 purchase totals = $1,088.99       $1,176.2000   $1,176.20   $1,176.25   $1,176.20