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 $244.28   13.279%   $276.7179   $276.72   $276.70   $276.70  
  Purchase #2 $77.45   6.323%   $82.3472   $82.35   $82.35   $82.30  
  Purchase #3 $115.52   6.103%   $122.5702   $122.57   $122.55   $122.60  
  Purchase #4 $175.92   7.342%   $188.836   $188.84   $188.85   $188.80  
  Purchase #5 $88.78   3.501%   $91.8882   $91.89   $91.90   $91.90  
  Purchase #6 $87.64   12.766%   $98.8281   $98.83   $98.85   $98.80  
  Purchase #7 $207.38   9.551%   $227.1869   $227.19   $227.20   $227.20  
  7 purchase totals = $996.97       $1,088.3745   $1,088.39   $1,088.40   $1,088.30