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 $160.45   10.257%   $176.9074   $176.91   $176.90   $176.90  
  Purchase #2 $93.91   11.417%   $104.6317   $104.63   $104.65   $104.60  
  Purchase #3 $199.87   6.116%   $212.094   $212.09   $212.10   $212.10  
  Purchase #4 $85.74   9.648%   $94.0122   $94.01   $94.00   $94.00  
  Purchase #5 $54.55   11.303%   $60.7158   $60.72   $60.70   $60.70  
  Purchase #6 $171.87   13.775%   $195.5451   $195.55   $195.55   $195.50  
  Purchase #7 $144.84   3.799%   $150.3425   $150.34   $150.35   $150.30  
  7 purchase totals = $911.23       $994.2487   $994.25   $994.25   $994.10