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 $50.98   5.333%   $53.6988   $53.70   $53.70   $53.70  
  Purchase #2 $188.47   7.839%   $203.2442   $203.24   $203.25   $203.20  
  Purchase #3 $146.74   6.662%   $156.5158   $156.52   $156.50   $156.50  
  Purchase #4 $250.99   5.860%   $265.698   $265.70   $265.70   $265.70  
  Purchase #5 $103.97   6.514%   $110.7426   $110.74   $110.75   $110.70  
  Purchase #6 $206.89   4.797%   $216.8145   $216.81   $216.80   $216.80  
  Purchase #7 $17.67   9.464%   $19.3423   $19.34   $19.35   $19.30  
  7 purchase totals = $965.71       $1,026.0562   $1,026.05   $1,026.05   $1,025.90