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 $137.95   13.147%   $156.0863   $156.09   $156.10   $156.10  
  Purchase #2 $216.26   4.393%   $225.7603   $225.76   $225.75   $225.80  
  Purchase #3 $203.55   5.464%   $214.672   $214.67   $214.65   $214.70  
  Purchase #4 $240.76   6.699%   $256.8885   $256.89   $256.90   $256.90  
  Purchase #5 $52.29   8.602%   $56.788   $56.79   $56.80   $56.80  
  Purchase #6 $152.87   13.318%   $173.2292   $173.23   $173.25   $173.20  
  Purchase #7 $166.75   7.740%   $179.6565   $179.66   $179.65   $179.70  
  7 purchase totals = $1,170.43       $1,263.0808   $1,263.09   $1,263.10   $1,263.20