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 $89.60   5.581%   $94.6006   $94.60   $94.60   $94.60  
  Purchase #2 $142.31   7.118%   $152.4396   $152.44   $152.45   $152.40  
  Purchase #3 $104.77   7.191%   $112.304   $112.30   $112.30   $112.30  
  Purchase #4 $187.73   9.871%   $206.2608   $206.26   $206.25   $206.30  
  Purchase #5 $75.87   8.239%   $82.1209   $82.12   $82.10   $82.10  
  Purchase #6 $167.44   8.361%   $181.4397   $181.44   $181.45   $181.40  
  Purchase #7 $123.73   11.624%   $138.1124   $138.11   $138.10   $138.10  
  7 purchase totals = $891.45       $967.2780   $967.27   $967.25   $967.20