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 $55.90   6.316%   $59.4306   $59.43   $59.45   $59.40  
  Purchase #2 $206.66   10.445%   $228.2456   $228.25   $228.25   $228.20  
  Purchase #3 $237.56   13.418%   $269.4358   $269.44   $269.45   $269.40  
  Purchase #4 $26.38   8.108%   $28.5189   $28.52   $28.50   $28.50  
  Purchase #5 $71.61   12.182%   $80.3335   $80.33   $80.35   $80.30  
  Purchase #6 $213.87   6.473%   $227.7138   $227.71   $227.70   $227.70  
  Purchase #7 $8.73   3.631%   $9.047   $9.05   $9.05   $9.00  
  7 purchase totals = $820.71       $902.7252   $902.73   $902.75   $902.50