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 $39.66   11.671%   $44.2887   $44.29   $44.30   $44.30  
  Purchase #2 $111.93   9.718%   $122.8074   $122.81   $122.80   $122.80  
  Purchase #3 $184.27   8.601%   $200.1191   $200.12   $200.10   $200.10  
  Purchase #4 $38.26   11.656%   $42.7196   $42.72   $42.70   $42.70  
  Purchase #5 $34.45   12.767%   $38.8482   $38.85   $38.85   $38.80  
  Purchase #6 $66.62   6.354%   $70.853   $70.85   $70.85   $70.90  
  Purchase #7 $183.68   11.508%   $204.8179   $204.82   $204.80   $204.80  
  7 purchase totals = $658.87       $724.4539   $724.46   $724.40   $724.40