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 $187.39   8.149%   $202.6604   $202.66   $202.65   $202.70  
  Purchase #2 $94.95   12.303%   $106.6317   $106.63   $106.65   $106.60  
  Purchase #3 $5.69   4.256%   $5.9322   $5.93   $5.95   $5.90  
  Purchase #4 $168.37   8.111%   $182.0265   $182.03   $182.05   $182.00  
  Purchase #5 $161.91   9.730%   $177.6638   $177.66   $177.65   $177.70  
  Purchase #6 $172.44   3.555%   $178.5702   $178.57   $178.55   $178.60  
  Purchase #7 $234.34   6.252%   $248.9909   $248.99   $249.00   $249.00  
  7 purchase totals = $1,025.09       $1,102.4757   $1,102.47   $1,102.50   $1,102.50