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 $174.90   12.249%   $196.3235   $196.32   $196.30   $196.30  
  Purchase #2 $216.57   13.629%   $246.0863   $246.09   $246.10   $246.10  
  Purchase #3 $166.99   6.699%   $178.1767   $178.18   $178.20   $178.20  
  Purchase #4 $119.80   6.658%   $127.7763   $127.78   $127.80   $127.80  
  Purchase #5 $191.74   8.571%   $208.174   $208.17   $208.15   $208.20  
  Purchase #6 $239.72   11.199%   $266.5662   $266.57   $266.55   $266.60  
  Purchase #7 $12.82   7.147%   $13.7362   $13.74   $13.75   $13.70  
  7 purchase totals = $1,122.54       $1,236.8392   $1,236.85   $1,236.85   $1,236.90