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 $16.58   3.767%   $17.2046   $17.20   $17.20   $17.20  
  Purchase #2 $206.58   11.143%   $229.5992   $229.60   $229.60   $229.60  
  Purchase #3 $60.81   8.684%   $66.0907   $66.09   $66.10   $66.10  
  Purchase #4 $79.31   4.276%   $82.7013   $82.70   $82.70   $82.70  
  Purchase #5 $218.47   12.631%   $246.0649   $246.06   $246.05   $246.10  
  Purchase #6 $118.82   9.592%   $130.2172   $130.22   $130.20   $130.20  
  Purchase #7 $191.59   6.533%   $204.1066   $204.11   $204.10   $204.10  
  7 purchase totals = $892.16       $975.9845   $975.98   $975.95   $976.00