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 $168.65   13.569%   $191.5341   $191.53   $191.55   $191.50  
  Purchase #2 $53.34   12.515%   $60.0155   $60.02   $60.00   $60.00  
  Purchase #3 $140.71   9.283%   $153.7721   $153.77   $153.75   $153.80  
  Purchase #4 $51.62   7.204%   $55.3387   $55.34   $55.35   $55.30  
  Purchase #5 $222.53   5.189%   $234.0771   $234.08   $234.10   $234.10  
  Purchase #6 $150.79   9.126%   $164.5511   $164.55   $164.55   $164.60  
  Purchase #7 $121.27   5.106%   $127.462   $127.46   $127.45   $127.50  
  7 purchase totals = $908.91       $986.7506   $986.75   $986.75   $986.80