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 $88.98   7.339%   $95.5102   $95.51   $95.50   $95.50  
  Purchase #2 $41.53   4.384%   $43.3507   $43.35   $43.35   $43.40  
  Purchase #3 $151.96   5.440%   $160.2266   $160.23   $160.25   $160.20  
  Purchase #4 $17.68   5.232%   $18.605   $18.61   $18.60   $18.60  
  Purchase #5 $15.64   5.386%   $16.4824   $16.48   $16.50   $16.50  
  Purchase #6 $93.51   8.536%   $101.492   $101.49   $101.50   $101.50  
  Purchase #7 $250.60   6.673%   $267.3225   $267.32   $267.30   $267.30  
  7 purchase totals = $659.90       $702.9894   $702.99   $703.00   $703.00