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 $194.57   9.247%   $212.5619   $212.56   $212.55   $212.60  
  Purchase #2 $244.25   3.153%   $251.9512   $251.95   $251.95   $252.00  
  Purchase #3 $13.44   11.798%   $15.0257   $15.03   $15.05   $15.00  
  Purchase #4 $92.56   11.312%   $103.0304   $103.03   $103.05   $103.00  
  Purchase #5 $166.58   13.866%   $189.678   $189.68   $189.70   $189.70  
  Purchase #6 $236.26   12.255%   $265.2137   $265.21   $265.20   $265.20  
  Purchase #7 $236.34   4.220%   $246.3135   $246.31   $246.30   $246.30  
  7 purchase totals = $1,184.00       $1,283.7744   $1,283.77   $1,283.80   $1,283.80