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 $64.66   6.282%   $68.7219   $68.72   $68.70   $68.70  
  Purchase #2 $93.79   10.207%   $103.3631   $103.36   $103.35   $103.40  
  Purchase #3 $70.30   10.757%   $77.8622   $77.86   $77.85   $77.90  
  Purchase #4 $220.31   9.813%   $241.929   $241.93   $241.95   $241.90  
  Purchase #5 $206.81   10.685%   $228.9076   $228.91   $228.90   $228.90  
  Purchase #6 $15.81   5.498%   $16.6792   $16.68   $16.70   $16.70  
  Purchase #7 $203.66   3.260%   $210.2993   $210.30   $210.30   $210.30  
  7 purchase totals = $875.34       $947.7623   $947.76   $947.75   $947.80