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 $189.85   3.336%   $196.1834   $196.18   $196.20   $196.20  
  Purchase #2 $15.88   4.249%   $16.5547   $16.55   $16.55   $16.60  
  Purchase #3 $113.93   11.730%   $127.294   $127.29   $127.30   $127.30  
  Purchase #4 $238.63   6.182%   $253.3821   $253.38   $253.40   $253.40  
  Purchase #5 $118.40   9.679%   $129.8599   $129.86   $129.85   $129.90  
  Purchase #6 $202.25   11.363%   $225.2317   $225.23   $225.25   $225.20  
  Purchase #7 $24.92   8.377%   $27.0075   $27.01   $27.00   $27.00  
  7 purchase totals = $903.86       $975.5133   $975.50   $975.55   $975.60