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 $44.33   12.484%   $49.8642   $49.86   $49.85   $49.90  
  Purchase #2 $179.65   12.258%   $201.6715   $201.67   $201.65   $201.70  
  Purchase #3 $98.53   12.791%   $111.133   $111.13   $111.15   $111.10  
  Purchase #4 $60.91   13.756%   $69.2888   $69.29   $69.30   $69.30  
  Purchase #5 $185.57   9.497%   $203.1936   $203.19   $203.20   $203.20  
  Purchase #6 $214.25   12.120%   $240.2171   $240.22   $240.20   $240.20  
  Purchase #7 $236.28   5.763%   $249.8968   $249.90   $249.90   $249.90  
  7 purchase totals = $1,019.52       $1,125.2650   $1,125.26   $1,125.25   $1,125.30