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 $38.74   10.265%   $42.7167   $42.72   $42.70   $42.70  
  Purchase #2 $50.68   13.727%   $57.6368   $57.64   $57.65   $57.60  
  Purchase #3 $42.93   5.253%   $45.1851   $45.19   $45.20   $45.20  
  Purchase #4 $193.99   5.216%   $204.1085   $204.11   $204.10   $204.10  
  Purchase #5 $209.89   5.169%   $220.7392   $220.74   $220.75   $220.70  
  Purchase #6 $240.34   11.203%   $267.2653   $267.27   $267.25   $267.30  
  Purchase #7 $174.55   6.726%   $186.2902   $186.29   $186.30   $186.30  
  7 purchase totals = $951.12       $1,023.9418   $1,023.96   $1,023.95   $1,023.90